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mm: zswap: remove same_filled module params

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These knobs offer more fine-grained control to userspace than needed and
directly expose/influence kernel implementation; remove them.

For disabling same_filled handling, there is no logical reason to refuse
storing same-filled pages more efficiently and opt for compression. 
Scanning pages for patterns may be an argument, but the page contents will
be read into the CPU cache anyway during compression.  Also, removing the
same_filled handling code does not move the needle significantly in terms
of performance anyway [1].

For disabling non_same_filled handling, it was added when the compressed
pages in zswap were not being properly charged to memcgs, as workloads
could escape the accounting with compression [2].  This is no longer the
case after commit f4840ccfca ("zswap: memcg accounting"), and using
zswap without compression does not make much sense.

[1]https://lore.kernel.org/lkml/CAJD7tkaySFP2hBQw4pnZHJJwe3bMdjJ1t9VC2VJd=khn1_TXvA@mail.gmail.com/
[2]https://lore.kernel.org/lkml/19d5cdee-2868-41bd-83d5-6da75d72e940@maciej.szmigiero.name/

[yosryahmed@google.com: remove same_filled_pages from docs]
  Link: https://lkml.kernel.org/r/ZhxFVggdyvCo79jc@google.com
Link: https://lkml.kernel.org/r/20240413022407.785696-5-yosryahmed@google.com
Signed-off-by: Yosry Ahmed <yosryahmed@google.com>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Nhat Pham <nphamcs@gmail.com>
Reviewed-by: Chengming Zhou <chengming.zhou@linux.dev>
Cc: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Yosry Ahmed 2024-04-13 02:24:07 +00:00 committed by Andrew Morton
parent e87b881489
commit c074e1467f
3 changed files with 0 additions and 50 deletions
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29
Documentation/admin-guide/mm/zswap.rst
View file

@ -111,35 +111,6 @@ checked if it is a same-value filled page before compressing it. If true, the
compressed length of the page is set to zero and the pattern or same-filled
value is stored.
Same-value filled pages identification feature is enabled by default and can be
disabled at boot time by setting the ``same_filled_pages_enabled`` attribute
to 0, e.g. ``zswap.same_filled_pages_enabled=0``. It can also be enabled and
disabled at runtime using the sysfs ``same_filled_pages_enabled``
attribute, e.g.::
echo 1 > /sys/module/zswap/parameters/same_filled_pages_enabled
When zswap same-filled page identification is disabled at runtime, it will stop
checking for the same-value filled pages during store operation.
In other words, every page will be then considered non-same-value filled.
However, the existing pages which are marked as same-value filled pages remain
stored unchanged in zswap until they are either loaded or invalidated.
In some circumstances it might be advantageous to make use of just the zswap
ability to efficiently store same-filled pages without enabling the whole
compressed page storage.
In this case the handling of non-same-value pages by zswap (enabled by default)
can be disabled by setting the ``non_same_filled_pages_enabled`` attribute
to 0, e.g. ``zswap.non_same_filled_pages_enabled=0``.
It can also be enabled and disabled at runtime using the sysfs
``non_same_filled_pages_enabled`` attribute, e.g.::
echo 1 > /sys/module/zswap/parameters/non_same_filled_pages_enabled
Disabling both ``zswap.same_filled_pages_enabled`` and
``zswap.non_same_filled_pages_enabled`` effectively disables accepting any new
pages by zswap.
To prevent zswap from shrinking pool when zswap is full and there's a high
pressure on swap (this will result in flipping pages in and out zswap pool
without any real benefit but with a performance drop for the system), a

2
Documentation/driver-api/crypto/iaa/iaa-crypto.rst
View file

@ -457,7 +457,6 @@ Use the following commands to enable zswap::
# echo deflate-iaa > /sys/module/zswap/parameters/compressor
# echo zsmalloc > /sys/module/zswap/parameters/zpool
# echo 1 > /sys/module/zswap/parameters/enabled
# echo 0 > /sys/module/zswap/parameters/same_filled_pages_enabled
# echo 100 > /proc/sys/vm/swappiness
# echo never > /sys/kernel/mm/transparent_hugepage/enabled
# echo 1 > /proc/sys/vm/overcommit_memory
@ -599,7 +598,6 @@ the 'fixed' compression mode::
echo deflate-iaa > /sys/module/zswap/parameters/compressor
echo zsmalloc > /sys/module/zswap/parameters/zpool
echo 1 > /sys/module/zswap/parameters/enabled
echo 0 > /sys/module/zswap/parameters/same_filled_pages_enabled
echo 100 > /proc/sys/vm/swappiness
echo never > /sys/kernel/mm/transparent_hugepage/enabled

19
mm/zswap.c
View file

@ -123,19 +123,6 @@ static unsigned int zswap_accept_thr_percent = 90; /* of max pool size */
module_param_named(accept_threshold_percent, zswap_accept_thr_percent,
uint, 0644);
/*
* Enable/disable handling same-value filled pages (enabled by default).
* If disabled every page is considered non-same-value filled.
*/
static bool zswap_same_filled_pages_enabled = true;
module_param_named(same_filled_pages_enabled, zswap_same_filled_pages_enabled,
bool, 0644);
/* Enable/disable handling non-same-value filled pages (enabled by default) */
static bool zswap_non_same_filled_pages_enabled = true;
module_param_named(non_same_filled_pages_enabled, zswap_non_same_filled_pages_enabled,
bool, 0644);
/* Number of zpools in zswap_pool (empirically determined for scalability) */
#define ZSWAP_NR_ZPOOLS 32
@ -1393,9 +1380,6 @@ static bool zswap_is_folio_same_filled(struct folio *folio, unsigned long *value
unsigned int pos, last_pos = PAGE_SIZE / sizeof(*page) - 1;
bool ret = false;
if (!zswap_same_filled_pages_enabled)
return false;
page = kmap_local_folio(folio, 0);
val = page[0];
@ -1473,9 +1457,6 @@ bool zswap_store(struct folio *folio)
goto store_entry;
}
if (!zswap_non_same_filled_pages_enabled)
goto freepage;
/* if entry is successfully added, it keeps the reference */
entry->pool = zswap_pool_current_get();
if (!entry->pool)