Messages in this thread | | | Date | Fri, 30 Jan 2015 16:30:49 +0300 | From | Konstantin Khlebnikov <> | Subject | Re: [PATCH] mm: don't account shared file pages in user_reserve_pages |
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On 29.01.2015 23:11, Andrew Shewmaker wrote: > On Thu, Jan 29, 2015 at 02:51:27PM +0300, Roman Gushchin wrote: >> Shared file pages are never accounted in memory overcommit code, >> so it isn't reasonable to count them in a code that limits the >> maximal size of a process in OVERCOMMIT_NONE mode. >> >> If a process has few large file mappings, the consequent attempts >> to allocate anonymous memory may unexpectedly fail with -ENOMEM, >> while there is free memory and overcommit limit if significantly >> larger than the committed amount (as displayed in /proc/meminfo). >> >> The problem is significantly smoothed by commit c9b1d0981fcc >> ("mm: limit growth of 3% hardcoded other user reserve"), >> which limits the impact of this check with 128Mb (tunable via sysctl), >> but it can still be a problem on small machines. >> >> Signed-off-by: Roman Gushchin <klamm@yandex-team.ru> >> Cc: Andrew Morton <akpm@linux-foundation.org> >> Cc: Andrew Shewmaker <agshew@gmail.com> >> Cc: Rik van Riel <riel@redhat.com> >> Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru> >> --- >> mm/mmap.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/mm/mmap.c b/mm/mmap.c >> index 7f684d5..151fadf 100644 >> --- a/mm/mmap.c >> +++ b/mm/mmap.c >> @@ -220,7 +220,7 @@ int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin) >> */ >> if (mm) { >> reserve = sysctl_user_reserve_kbytes >> (PAGE_SHIFT - 10); >> - allowed -= min(mm->total_vm / 32, reserve); >> + allowed -= min((mm->total_vm - mm->shared_vm) / 32, reserve); >> } >> >> if (percpu_counter_read_positive(&vm_committed_as) < allowed) >> -- >> 2.1.0 > > You're two patches conflict, don't they? Maybe you should resend > them as a patch series such that they can both be applied?
I think arithmetic overflow is more important. Upper bound 128M for user reserve makes mis-accounting of shared memory mostly invisible.
> > Does mm->shared_vm include memory that's mapped MAP_ANONYMOUS in > conjunction with MAP_SHARED? If so, then subtracting it could > overcommit the system OVERCOMMIT_NEVER mode.
Yep.
Moreover shared_vm also includes file mappings with MAP_PRIVATE. It works more likely as "maybe shared", upper bound for "file-rss" (MM_FILEPAGES).
I think we need here total size of vmas where VM_ACCOUNT is set -- writable private mappings mapped without MAP_NORESERVE or something like that. But total_vm after limiting with 128Mb gives almost always the same or similar value. So, let's keep it as is.
-- Konstantin
> > -Andrew >
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