On 2017/5/24 18:32, Vlastimil Babka wrote:
> On 05/24/2017 10:32 AM, Yisheng Xie wrote:
>> Hi Kefeng，
>> Could you please try this patch.
>>
>> Thanks
>> Yisheng Xie
>> -------------
>> From a70ae975756e8e97a28d49117ab25684da631689 Mon Sep 17 00:00:00 2001
>> From: Yisheng Xie <xieyisheng1@xxxxxxxxxx>
>> Date: Wed, 24 May 2017 16:01:24 +0800
>> Subject: [PATCH] mlock: fix mlock count can not decrease in race condition
>>
>> Kefeng reported that when run the follow test the mlock count in meminfo
>> cannot be decreased:
>> [1] testcase
>> linux:~ # cat test_mlockal
>> grep Mlocked /proc/meminfo
>> for j in `seq 0 10`
>> do
>> for i in `seq 4 15`
>> do
>> ./p_mlockall >> log &
>> done
>> sleep 0.2
>> done
>> sleep 5 # wait some time to let mlock decrease
>> grep Mlocked /proc/meminfo
>>
>> linux:~ # cat p_mlockall.c
>> #include <sys/mman.h>
>> #include <stdlib.h>
>> #include <stdio.h>
>>
>> #define SPACE_LEN 4096
>>
>> int main(int argc, char ** argv)
>> {
>> int ret;
>> void *adr = malloc(SPACE_LEN);
>> if (!adr)
>> return -1;
>>
>> ret = mlockall(MCL_CURRENT | MCL_FUTURE);
>> printf("mlcokall ret = %d\n", ret);
>>
>> ret = munlockall();
>> printf("munlcokall ret = %d\n", ret);
>>
>> free(adr);
>> return 0;
>> }
>>
>> When __munlock_pagevec, we ClearPageMlock but isolation_failed in race
>> condition, and we do not count these page into delta_munlocked, which cause mlock
>
> Race condition with what? Who else would isolate our pages?
>
Hi Vlastimil,
I find the root cause, if the page was not cached on the current cpu,
lru_add_drain() will not push it to LRU. So we should handle fail
case in mlock_vma_page().
follow_page_pte()
...
if (page->mapping && trylock_page(page)) {
lru_add_drain(); /* push cached pages to LRU */
/*
* Because we lock page here, and migration is
* blocked by the pte's page reference, and we
* know the page is still mapped, we don't even
* need to check for file-cache page truncation.
*/
mlock_vma_page(page);
unlock_page(page);
}
...
I think we should add yisheng's patch, also we should add the following change.
I think it is better than use lru_add_drain_all().
diff --git a/mm/mlock.c b/mm/mlock.c
index 3d3ee6c..ca2aeb9 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -88,6 +88,11 @@ void mlock_vma_page(struct page *page)
count_vm_event(UNEVICTABLE_PGMLOCKED);
if (!isolate_lru_page(page))
putback_lru_page(page);
+ else {
+ ClearPageMlocked(page);
+ mod_zone_page_state(page_zone(page), NR_MLOCK,
+ -hpage_nr_pages(page));
+ }
}
}
Thanks,
Xishi Qiu
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