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![Nhat Pham](/assets/img/avatar_default.png)
During our experiment with zswap, we sometimes observe swap IOs due to occasional zswap store failures and writebacks-to-swap. These swapping IOs prevent many users who cannot tolerate swapping from adopting zswap to save memory and improve performance where possible. This patch adds the option to disable this behavior entirely: do not writeback to backing swapping device when a zswap store attempt fail, and do not write pages in the zswap pool back to the backing swap device (both when the pool is full, and when the new zswap shrinker is called). This new behavior can be opted-in/out on a per-cgroup basis via a new cgroup file. By default, writebacks to swap device is enabled, which is the previous behavior. Initially, writeback is enabled for the root cgroup, and a newly created cgroup will inherit the current setting of its parent. Note that this is subtly different from setting memory.swap.max to 0, as it still allows for pages to be stored in the zswap pool (which itself consumes swap space in its current form). This patch should be applied on top of the zswap shrinker series: https://lore.kernel.org/linux-mm/20231130194023.4102148-1-nphamcs@gmail.com/ as it also disables the zswap shrinker, a major source of zswap writebacks. For the most part, this feature is motivated by internal parties who have already established their opinions regarding swapping - the workloads that are highly sensitive to IO, and especially those who are using servers with really slow disk performance (for instance, massive but slow HDDs). For these folks, it's impossible to convince them to even entertain zswap if swapping also comes as a packaged deal. Writeback disabling is quite a useful feature in these situations - on a mixed workloads deployment, they can disable writeback for the more IO-sensitive workloads, and enable writeback for other background workloads. For instance, on a server with HDD, I allocate memories and populate them with random values (so that zswap store will always fail), and specify memory.high low enough to trigger reclaim. The time it takes to allocate the memories and just read through it a couple of times (doing silly things like computing the values' average etc.): zswap.writeback disabled: real 0m30.537s user 0m23.687s sys 0m6.637s 0 pages swapped in 0 pages swapped out zswap.writeback enabled: real 0m45.061s user 0m24.310s sys 0m8.892s 712686 pages swapped in 461093 pages swapped out (the last two lines are from vmstat -s). [nphamcs@gmail.com: add a comment about recurring zswap store failures leading to reclaim inefficiency] Link: https://lkml.kernel.org/r/20231221005725.3446672-1-nphamcs@gmail.com Link: https://lkml.kernel.org/r/20231207192406.3809579-1-nphamcs@gmail.com Signed-off-by: Nhat Pham <nphamcs@gmail.com> Suggested-by: Johannes Weiner <hannes@cmpxchg.org> Reviewed-by: Yosry Ahmed <yosryahmed@google.com> Acked-by: Chris Li <chrisl@kernel.org> Cc: Dan Streetman <ddstreet@ieee.org> Cc: David Heidelberg <david@ixit.cz> Cc: Domenico Cerasuolo <cerasuolodomenico@gmail.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Cc: Michal Hocko <mhocko@kernel.org> Cc: Mike Rapoport (IBM) <rppt@kernel.org> Cc: Muchun Song <muchun.song@linux.dev> Cc: Roman Gushchin <roman.gushchin@linux.dev> Cc: Sergey Senozhatsky <senozhatsky@chromium.org> Cc: Seth Jennings <sjenning@redhat.com> Cc: Shakeel Butt <shakeelb@google.com> Cc: Tejun Heo <tj@kernel.org> Cc: Vitaly Wool <vitaly.wool@konsulko.com> Cc: Zefan Li <lizefan.x@bytedance.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
547 lines
14 KiB
C
547 lines
14 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* linux/mm/page_io.c
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*
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* Copyright (C) 1991, 1992, 1993, 1994 Linus Torvalds
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*
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* Swap reorganised 29.12.95,
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* Asynchronous swapping added 30.12.95. Stephen Tweedie
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* Removed race in async swapping. 14.4.1996. Bruno Haible
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* Add swap of shared pages through the page cache. 20.2.1998. Stephen Tweedie
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* Always use brw_page, life becomes simpler. 12 May 1998 Eric Biederman
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*/
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#include <linux/mm.h>
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#include <linux/kernel_stat.h>
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#include <linux/gfp.h>
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#include <linux/pagemap.h>
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#include <linux/swap.h>
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#include <linux/bio.h>
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#include <linux/swapops.h>
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#include <linux/writeback.h>
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#include <linux/blkdev.h>
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#include <linux/psi.h>
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#include <linux/uio.h>
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#include <linux/sched/task.h>
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#include <linux/delayacct.h>
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#include <linux/zswap.h>
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#include "swap.h"
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static void __end_swap_bio_write(struct bio *bio)
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{
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struct folio *folio = bio_first_folio_all(bio);
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if (bio->bi_status) {
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/*
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* We failed to write the page out to swap-space.
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* Re-dirty the page in order to avoid it being reclaimed.
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* Also print a dire warning that things will go BAD (tm)
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* very quickly.
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*
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* Also clear PG_reclaim to avoid folio_rotate_reclaimable()
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*/
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folio_mark_dirty(folio);
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pr_alert_ratelimited("Write-error on swap-device (%u:%u:%llu)\n",
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MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
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(unsigned long long)bio->bi_iter.bi_sector);
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folio_clear_reclaim(folio);
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}
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folio_end_writeback(folio);
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}
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static void end_swap_bio_write(struct bio *bio)
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{
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__end_swap_bio_write(bio);
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bio_put(bio);
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}
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static void __end_swap_bio_read(struct bio *bio)
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{
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struct folio *folio = bio_first_folio_all(bio);
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if (bio->bi_status) {
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pr_alert_ratelimited("Read-error on swap-device (%u:%u:%llu)\n",
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MAJOR(bio_dev(bio)), MINOR(bio_dev(bio)),
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(unsigned long long)bio->bi_iter.bi_sector);
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} else {
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folio_mark_uptodate(folio);
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}
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folio_unlock(folio);
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}
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static void end_swap_bio_read(struct bio *bio)
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{
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__end_swap_bio_read(bio);
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bio_put(bio);
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}
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int generic_swapfile_activate(struct swap_info_struct *sis,
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struct file *swap_file,
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sector_t *span)
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{
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struct address_space *mapping = swap_file->f_mapping;
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struct inode *inode = mapping->host;
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unsigned blocks_per_page;
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unsigned long page_no;
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unsigned blkbits;
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sector_t probe_block;
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sector_t last_block;
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sector_t lowest_block = -1;
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sector_t highest_block = 0;
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int nr_extents = 0;
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int ret;
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blkbits = inode->i_blkbits;
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blocks_per_page = PAGE_SIZE >> blkbits;
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/*
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* Map all the blocks into the extent tree. This code doesn't try
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* to be very smart.
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*/
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probe_block = 0;
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page_no = 0;
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last_block = i_size_read(inode) >> blkbits;
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while ((probe_block + blocks_per_page) <= last_block &&
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page_no < sis->max) {
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unsigned block_in_page;
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sector_t first_block;
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cond_resched();
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first_block = probe_block;
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ret = bmap(inode, &first_block);
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if (ret || !first_block)
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goto bad_bmap;
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/*
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* It must be PAGE_SIZE aligned on-disk
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*/
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if (first_block & (blocks_per_page - 1)) {
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probe_block++;
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goto reprobe;
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}
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for (block_in_page = 1; block_in_page < blocks_per_page;
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block_in_page++) {
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sector_t block;
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block = probe_block + block_in_page;
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ret = bmap(inode, &block);
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if (ret || !block)
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goto bad_bmap;
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if (block != first_block + block_in_page) {
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/* Discontiguity */
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probe_block++;
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goto reprobe;
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}
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}
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first_block >>= (PAGE_SHIFT - blkbits);
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if (page_no) { /* exclude the header page */
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if (first_block < lowest_block)
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lowest_block = first_block;
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if (first_block > highest_block)
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highest_block = first_block;
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}
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/*
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* We found a PAGE_SIZE-length, PAGE_SIZE-aligned run of blocks
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*/
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ret = add_swap_extent(sis, page_no, 1, first_block);
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if (ret < 0)
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goto out;
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nr_extents += ret;
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page_no++;
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probe_block += blocks_per_page;
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reprobe:
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continue;
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}
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ret = nr_extents;
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*span = 1 + highest_block - lowest_block;
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if (page_no == 0)
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page_no = 1; /* force Empty message */
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sis->max = page_no;
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sis->pages = page_no - 1;
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sis->highest_bit = page_no - 1;
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out:
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return ret;
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bad_bmap:
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pr_err("swapon: swapfile has holes\n");
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ret = -EINVAL;
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goto out;
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}
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/*
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* We may have stale swap cache pages in memory: notice
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* them here and get rid of the unnecessary final write.
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*/
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int swap_writepage(struct page *page, struct writeback_control *wbc)
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{
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struct folio *folio = page_folio(page);
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int ret;
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if (folio_free_swap(folio)) {
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folio_unlock(folio);
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return 0;
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}
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/*
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* Arch code may have to preserve more data than just the page
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* contents, e.g. memory tags.
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*/
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ret = arch_prepare_to_swap(&folio->page);
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if (ret) {
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folio_mark_dirty(folio);
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folio_unlock(folio);
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return ret;
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}
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if (zswap_store(folio)) {
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folio_start_writeback(folio);
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folio_unlock(folio);
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folio_end_writeback(folio);
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return 0;
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}
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if (!mem_cgroup_zswap_writeback_enabled(folio_memcg(folio))) {
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folio_mark_dirty(folio);
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return AOP_WRITEPAGE_ACTIVATE;
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}
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__swap_writepage(folio, wbc);
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return 0;
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}
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static inline void count_swpout_vm_event(struct folio *folio)
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{
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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if (unlikely(folio_test_pmd_mappable(folio))) {
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count_memcg_folio_events(folio, THP_SWPOUT, 1);
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count_vm_event(THP_SWPOUT);
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}
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#endif
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count_vm_events(PSWPOUT, folio_nr_pages(folio));
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}
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#if defined(CONFIG_MEMCG) && defined(CONFIG_BLK_CGROUP)
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static void bio_associate_blkg_from_page(struct bio *bio, struct folio *folio)
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{
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struct cgroup_subsys_state *css;
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struct mem_cgroup *memcg;
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memcg = folio_memcg(folio);
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if (!memcg)
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return;
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rcu_read_lock();
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css = cgroup_e_css(memcg->css.cgroup, &io_cgrp_subsys);
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bio_associate_blkg_from_css(bio, css);
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rcu_read_unlock();
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}
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#else
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#define bio_associate_blkg_from_page(bio, folio) do { } while (0)
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#endif /* CONFIG_MEMCG && CONFIG_BLK_CGROUP */
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struct swap_iocb {
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struct kiocb iocb;
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struct bio_vec bvec[SWAP_CLUSTER_MAX];
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int pages;
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int len;
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};
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static mempool_t *sio_pool;
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int sio_pool_init(void)
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{
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if (!sio_pool) {
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mempool_t *pool = mempool_create_kmalloc_pool(
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SWAP_CLUSTER_MAX, sizeof(struct swap_iocb));
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if (cmpxchg(&sio_pool, NULL, pool))
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mempool_destroy(pool);
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}
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if (!sio_pool)
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return -ENOMEM;
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return 0;
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}
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static void sio_write_complete(struct kiocb *iocb, long ret)
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{
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struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
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struct page *page = sio->bvec[0].bv_page;
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int p;
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if (ret != sio->len) {
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/*
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* In the case of swap-over-nfs, this can be a
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* temporary failure if the system has limited
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* memory for allocating transmit buffers.
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* Mark the page dirty and avoid
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* folio_rotate_reclaimable but rate-limit the
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* messages but do not flag PageError like
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* the normal direct-to-bio case as it could
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* be temporary.
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*/
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pr_err_ratelimited("Write error %ld on dio swapfile (%llu)\n",
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ret, page_file_offset(page));
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for (p = 0; p < sio->pages; p++) {
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page = sio->bvec[p].bv_page;
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set_page_dirty(page);
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ClearPageReclaim(page);
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}
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}
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for (p = 0; p < sio->pages; p++)
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end_page_writeback(sio->bvec[p].bv_page);
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mempool_free(sio, sio_pool);
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}
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static void swap_writepage_fs(struct folio *folio, struct writeback_control *wbc)
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{
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struct swap_iocb *sio = NULL;
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struct swap_info_struct *sis = swp_swap_info(folio->swap);
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struct file *swap_file = sis->swap_file;
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loff_t pos = folio_file_pos(folio);
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count_swpout_vm_event(folio);
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folio_start_writeback(folio);
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folio_unlock(folio);
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if (wbc->swap_plug)
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sio = *wbc->swap_plug;
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if (sio) {
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if (sio->iocb.ki_filp != swap_file ||
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sio->iocb.ki_pos + sio->len != pos) {
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swap_write_unplug(sio);
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sio = NULL;
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}
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}
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if (!sio) {
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sio = mempool_alloc(sio_pool, GFP_NOIO);
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init_sync_kiocb(&sio->iocb, swap_file);
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sio->iocb.ki_complete = sio_write_complete;
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sio->iocb.ki_pos = pos;
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sio->pages = 0;
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sio->len = 0;
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}
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bvec_set_folio(&sio->bvec[sio->pages], folio, folio_size(folio), 0);
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sio->len += folio_size(folio);
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sio->pages += 1;
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if (sio->pages == ARRAY_SIZE(sio->bvec) || !wbc->swap_plug) {
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swap_write_unplug(sio);
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sio = NULL;
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}
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if (wbc->swap_plug)
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*wbc->swap_plug = sio;
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}
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static void swap_writepage_bdev_sync(struct folio *folio,
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struct writeback_control *wbc, struct swap_info_struct *sis)
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{
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struct bio_vec bv;
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struct bio bio;
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bio_init(&bio, sis->bdev, &bv, 1,
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REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc));
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bio.bi_iter.bi_sector = swap_folio_sector(folio);
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bio_add_folio_nofail(&bio, folio, folio_size(folio), 0);
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bio_associate_blkg_from_page(&bio, folio);
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count_swpout_vm_event(folio);
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folio_start_writeback(folio);
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folio_unlock(folio);
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submit_bio_wait(&bio);
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__end_swap_bio_write(&bio);
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}
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static void swap_writepage_bdev_async(struct folio *folio,
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struct writeback_control *wbc, struct swap_info_struct *sis)
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{
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struct bio *bio;
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bio = bio_alloc(sis->bdev, 1,
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REQ_OP_WRITE | REQ_SWAP | wbc_to_write_flags(wbc),
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GFP_NOIO);
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bio->bi_iter.bi_sector = swap_folio_sector(folio);
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bio->bi_end_io = end_swap_bio_write;
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bio_add_folio_nofail(bio, folio, folio_size(folio), 0);
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bio_associate_blkg_from_page(bio, folio);
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count_swpout_vm_event(folio);
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folio_start_writeback(folio);
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folio_unlock(folio);
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submit_bio(bio);
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}
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void __swap_writepage(struct folio *folio, struct writeback_control *wbc)
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{
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struct swap_info_struct *sis = swp_swap_info(folio->swap);
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VM_BUG_ON_FOLIO(!folio_test_swapcache(folio), folio);
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/*
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* ->flags can be updated non-atomicially (scan_swap_map_slots),
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* but that will never affect SWP_FS_OPS, so the data_race
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* is safe.
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*/
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if (data_race(sis->flags & SWP_FS_OPS))
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swap_writepage_fs(folio, wbc);
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else if (sis->flags & SWP_SYNCHRONOUS_IO)
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swap_writepage_bdev_sync(folio, wbc, sis);
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else
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swap_writepage_bdev_async(folio, wbc, sis);
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}
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void swap_write_unplug(struct swap_iocb *sio)
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{
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struct iov_iter from;
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struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
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int ret;
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iov_iter_bvec(&from, ITER_SOURCE, sio->bvec, sio->pages, sio->len);
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ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
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if (ret != -EIOCBQUEUED)
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sio_write_complete(&sio->iocb, ret);
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}
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static void sio_read_complete(struct kiocb *iocb, long ret)
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{
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struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
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int p;
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if (ret == sio->len) {
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for (p = 0; p < sio->pages; p++) {
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struct folio *folio = page_folio(sio->bvec[p].bv_page);
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folio_mark_uptodate(folio);
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folio_unlock(folio);
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}
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count_vm_events(PSWPIN, sio->pages);
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} else {
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for (p = 0; p < sio->pages; p++) {
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struct folio *folio = page_folio(sio->bvec[p].bv_page);
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folio_unlock(folio);
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}
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pr_alert_ratelimited("Read-error on swap-device\n");
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}
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mempool_free(sio, sio_pool);
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}
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static void swap_read_folio_fs(struct folio *folio, struct swap_iocb **plug)
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{
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struct swap_info_struct *sis = swp_swap_info(folio->swap);
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struct swap_iocb *sio = NULL;
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loff_t pos = folio_file_pos(folio);
|
|
|
|
if (plug)
|
|
sio = *plug;
|
|
if (sio) {
|
|
if (sio->iocb.ki_filp != sis->swap_file ||
|
|
sio->iocb.ki_pos + sio->len != pos) {
|
|
swap_read_unplug(sio);
|
|
sio = NULL;
|
|
}
|
|
}
|
|
if (!sio) {
|
|
sio = mempool_alloc(sio_pool, GFP_KERNEL);
|
|
init_sync_kiocb(&sio->iocb, sis->swap_file);
|
|
sio->iocb.ki_pos = pos;
|
|
sio->iocb.ki_complete = sio_read_complete;
|
|
sio->pages = 0;
|
|
sio->len = 0;
|
|
}
|
|
bvec_set_folio(&sio->bvec[sio->pages], folio, folio_size(folio), 0);
|
|
sio->len += folio_size(folio);
|
|
sio->pages += 1;
|
|
if (sio->pages == ARRAY_SIZE(sio->bvec) || !plug) {
|
|
swap_read_unplug(sio);
|
|
sio = NULL;
|
|
}
|
|
if (plug)
|
|
*plug = sio;
|
|
}
|
|
|
|
static void swap_read_folio_bdev_sync(struct folio *folio,
|
|
struct swap_info_struct *sis)
|
|
{
|
|
struct bio_vec bv;
|
|
struct bio bio;
|
|
|
|
bio_init(&bio, sis->bdev, &bv, 1, REQ_OP_READ);
|
|
bio.bi_iter.bi_sector = swap_folio_sector(folio);
|
|
bio_add_folio_nofail(&bio, folio, folio_size(folio), 0);
|
|
/*
|
|
* Keep this task valid during swap readpage because the oom killer may
|
|
* attempt to access it in the page fault retry time check.
|
|
*/
|
|
get_task_struct(current);
|
|
count_vm_event(PSWPIN);
|
|
submit_bio_wait(&bio);
|
|
__end_swap_bio_read(&bio);
|
|
put_task_struct(current);
|
|
}
|
|
|
|
static void swap_read_folio_bdev_async(struct folio *folio,
|
|
struct swap_info_struct *sis)
|
|
{
|
|
struct bio *bio;
|
|
|
|
bio = bio_alloc(sis->bdev, 1, REQ_OP_READ, GFP_KERNEL);
|
|
bio->bi_iter.bi_sector = swap_folio_sector(folio);
|
|
bio->bi_end_io = end_swap_bio_read;
|
|
bio_add_folio_nofail(bio, folio, folio_size(folio), 0);
|
|
count_vm_event(PSWPIN);
|
|
submit_bio(bio);
|
|
}
|
|
|
|
void swap_read_folio(struct folio *folio, bool synchronous,
|
|
struct swap_iocb **plug)
|
|
{
|
|
struct swap_info_struct *sis = swp_swap_info(folio->swap);
|
|
bool workingset = folio_test_workingset(folio);
|
|
unsigned long pflags;
|
|
bool in_thrashing;
|
|
|
|
VM_BUG_ON_FOLIO(!folio_test_swapcache(folio) && !synchronous, folio);
|
|
VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
|
|
VM_BUG_ON_FOLIO(folio_test_uptodate(folio), folio);
|
|
|
|
/*
|
|
* Count submission time as memory stall and delay. When the device
|
|
* is congested, or the submitting cgroup IO-throttled, submission
|
|
* can be a significant part of overall IO time.
|
|
*/
|
|
if (workingset) {
|
|
delayacct_thrashing_start(&in_thrashing);
|
|
psi_memstall_enter(&pflags);
|
|
}
|
|
delayacct_swapin_start();
|
|
|
|
if (zswap_load(folio)) {
|
|
folio_mark_uptodate(folio);
|
|
folio_unlock(folio);
|
|
} else if (data_race(sis->flags & SWP_FS_OPS)) {
|
|
swap_read_folio_fs(folio, plug);
|
|
} else if (synchronous || (sis->flags & SWP_SYNCHRONOUS_IO)) {
|
|
swap_read_folio_bdev_sync(folio, sis);
|
|
} else {
|
|
swap_read_folio_bdev_async(folio, sis);
|
|
}
|
|
|
|
if (workingset) {
|
|
delayacct_thrashing_end(&in_thrashing);
|
|
psi_memstall_leave(&pflags);
|
|
}
|
|
delayacct_swapin_end();
|
|
}
|
|
|
|
void __swap_read_unplug(struct swap_iocb *sio)
|
|
{
|
|
struct iov_iter from;
|
|
struct address_space *mapping = sio->iocb.ki_filp->f_mapping;
|
|
int ret;
|
|
|
|
iov_iter_bvec(&from, ITER_DEST, sio->bvec, sio->pages, sio->len);
|
|
ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
|
|
if (ret != -EIOCBQUEUED)
|
|
sio_read_complete(&sio->iocb, ret);
|
|
}
|