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 <[email protected]>
Cc: Andrew Morton <[email protected]>
Cc: Andrew Shewmaker <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Konstantin Khlebnikov <[email protected]>
---
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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
