linux/fs/proc
Michal Hocko 0ee931c4e3 mm: treewide: remove GFP_TEMPORARY allocation flag
GFP_TEMPORARY was introduced by commit e12ba74d8f ("Group short-lived
and reclaimable kernel allocations") along with __GFP_RECLAIMABLE.  It's
primary motivation was to allow users to tell that an allocation is
short lived and so the allocator can try to place such allocations close
together and prevent long term fragmentation.  As much as this sounds
like a reasonable semantic it becomes much less clear when to use the
highlevel GFP_TEMPORARY allocation flag.  How long is temporary? Can the
context holding that memory sleep? Can it take locks? It seems there is
no good answer for those questions.

The current implementation of GFP_TEMPORARY is basically GFP_KERNEL |
__GFP_RECLAIMABLE which in itself is tricky because basically none of
the existing caller provide a way to reclaim the allocated memory.  So
this is rather misleading and hard to evaluate for any benefits.

I have checked some random users and none of them has added the flag
with a specific justification.  I suspect most of them just copied from
other existing users and others just thought it might be a good idea to
use without any measuring.  This suggests that GFP_TEMPORARY just
motivates for cargo cult usage without any reasoning.

I believe that our gfp flags are quite complex already and especially
those with highlevel semantic should be clearly defined to prevent from
confusion and abuse.  Therefore I propose dropping GFP_TEMPORARY and
replace all existing users to simply use GFP_KERNEL.  Please note that
SLAB users with shrinkers will still get __GFP_RECLAIMABLE heuristic and
so they will be placed properly for memory fragmentation prevention.

I can see reasons we might want some gfp flag to reflect shorterm
allocations but I propose starting from a clear semantic definition and
only then add users with proper justification.

This was been brought up before LSF this year by Matthew [1] and it
turned out that GFP_TEMPORARY really doesn't have a clear semantic.  It
seems to be a heuristic without any measured advantage for most (if not
all) its current users.  The follow up discussion has revealed that
opinions on what might be temporary allocation differ a lot between
developers.  So rather than trying to tweak existing users into a
semantic which they haven't expected I propose to simply remove the flag
and start from scratch if we really need a semantic for short term
allocations.

[1] http://lkml.kernel.org/r/20170118054945.GD18349@bombadil.infradead.org

[akpm@linux-foundation.org: fix typo]
[akpm@linux-foundation.org: coding-style fixes]
[sfr@canb.auug.org.au: drm/i915: fix up]
  Link: http://lkml.kernel.org/r/20170816144703.378d4f4d@canb.auug.org.au
Link: http://lkml.kernel.org/r/20170728091904.14627-1-mhocko@kernel.org
Signed-off-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Neil Brown <neilb@suse.de>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2017-09-13 18:53:16 -07:00
..
array.c sched/headers: Prepare to move cputime functionality from <linux/sched.h> into <linux/sched/cputime.h> 2017-03-02 08:42:39 +01:00
base.c mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
cmdline.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
consoles.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
cpuinfo.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
devices.c block: order /proc/devices by major number 2017-07-17 15:42:20 +02:00
fd.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/signal.h> 2017-03-02 08:42:29 +01:00
fd.h proc: unsigned file descriptors 2016-09-27 18:47:38 -04:00
generic.c procfs: use faster rb_first_cached() 2017-09-08 18:26:49 -07:00
inode.c fs/proc/inode.c: remove cast from memory allocation 2017-05-08 17:15:10 -07:00
internal.h procfs: use faster rb_first_cached() 2017-09-08 18:26:49 -07:00
interrupts.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
Kconfig fs, proc: add help for CONFIG_PROC_CHILDREN 2015-07-17 16:39:52 -07:00
kcore.c fs/proc: kcore: use kcore_list type to check for vmalloc/module address 2017-06-20 12:42:57 +01:00
kmsg.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
loadavg.c sched/headers: Prepare for new header dependencies before moving code to <linux/sched/stat.h> 2017-03-02 08:42:34 +01:00
Makefile fs/proc: Add compiler check for -Wno-override-init to support gcc < 4.2 2016-08-03 12:45:23 -04:00
meminfo.c mm: rename global_page_state to global_zone_page_state 2017-09-06 17:27:29 -07:00
namespaces.c pidns: expose task pid_ns_for_children to userspace 2017-05-08 17:15:12 -07:00
nommu.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
page.c mm: fix KPF_SWAPCACHE in /proc/kpageflags 2017-02-07 12:08:32 -08:00
proc_net.c procfs: use faster rb_first_cached() 2017-09-08 18:26:49 -07:00
proc_sysctl.c Merge branch 'akpm' (patches from Andrew) 2017-07-13 12:38:49 -07:00
proc_tty.c Replace <asm/uaccess.h> with <linux/uaccess.h> globally 2016-12-24 11:46:01 -08:00
root.c procfs: use faster rb_first_cached() 2017-09-08 18:26:49 -07:00
self.c vfs: remove ".readlink = generic_readlink" assignments 2016-12-09 16:45:04 +01:00
softirqs.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
stat.c sched/headers: Prepare to move cputime functionality from <linux/sched.h> into <linux/sched/cputime.h> 2017-03-02 08:42:39 +01:00
task_mmu.c mm: treewide: remove GFP_TEMPORARY allocation flag 2017-09-13 18:53:16 -07:00
task_nommu.c procfs: remove unused variable 2017-09-13 18:53:15 -07:00
thread_self.c vfs: remove ".readlink = generic_readlink" assignments 2016-12-09 16:45:04 +01:00
uptime.c sched/cputime: Convert kcpustat to nsecs 2017-02-01 09:13:47 +01:00
version.c fs/proc: don't use module_init for non-modular core code 2014-01-23 16:37:02 -08:00
vmcore.c userfaultfd: non-cooperative: add event for memory unmaps 2017-02-24 17:46:55 -08:00