linux-kernel - Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

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Date:	Fri, 20 May 2011 14:36:13 +0900
From:	Minchan Kim <minchan.kim@...il.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Andrew Lutomirski <luto@....edu>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	fengguang.wu@...el.com, andi@...stfloor.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, mgorman@...e.de, hannes@...xchg.org,
	riel@...hat.com
Subject: Re: Kernel falls apart under light memory pressure (i.e. linking vmlinux)

On Fri, May 20, 2011 at 2:08 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> On Fri, 20 May 2011 13:20:15 +0900
> Minchan Kim <minchan.kim@...il.com> wrote:
>
>> So I want to resolve your problem asap.
>> We don't have see report about that. Could you do git-bisect?
>> FYI, Recently, big change of mm is compaction,transparent huge pages.
>> Kame, could you point out thing related to memcg if you have a mind?
>>
>
> I don't doubt memcg at this stage because it never modify page->flags.
> Consdering the case, PageActive() is set against off-LRU pages after
> clear_active_flags() clears it.
>
> Hmm, I think I don't understand the lock system fully but...how do you
> think this ?
>
> ==
>
> At splitting a hugepage, the routine marks all pmd as "splitting".
>
> But assume a racy case where 2 threads run into spit at the
> same time, one thread wins compound_lock() and do split, another
> thread should not touch splitted pages.

Sorry. Now I don't have a time to review in detail.
When I look it roughly,  page_lock_anon_vma have to prevent it.
But Andrea needs current this problem and he will catch something we lost. :)


>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Index: mmotm-May11/mm/huge_memory.c
> ===================================================================
> --- mmotm-May11.orig/mm/huge_memory.c
> +++ mmotm-May11/mm/huge_memory.c
> @@ -1150,7 +1150,7 @@ static int __split_huge_page_splitting(s
>        return ret;
>  }
>
> -static void __split_huge_page_refcount(struct page *page)
> +static bool __split_huge_page_refcount(struct page *page)
>  {
>        int i;
>        unsigned long head_index = page->index;
> @@ -1161,6 +1161,11 @@ static void __split_huge_page_refcount(s
>        spin_lock_irq(&zone->lru_lock);
>        compound_lock(page);
>
> +       if (!PageCompound(page)) {
> +               compound_unlock(page);
> +               spin_unlock_irq(&zone->lru_lock);
> +               return false;
> +       }
>        for (i = 1; i < HPAGE_PMD_NR; i++) {
>                struct page *page_tail = page + i;
>
> @@ -1258,6 +1263,7 @@ static void __split_huge_page_refcount(s
>         * to be pinned by the caller.
>         */
>        BUG_ON(page_count(page) <= 0);
> +       return true;
>  }
>
>  static int __split_huge_page_map(struct page *page,
> @@ -1367,7 +1373,8 @@ static void __split_huge_page(struct pag
>                       mapcount, page_mapcount(page));
>        BUG_ON(mapcount != page_mapcount(page));
>
> -       __split_huge_page_refcount(page);
> +       if (!__split_huge_page_refcount(page))
> +               return;
>
>        mapcount2 = 0;
>        list_for_each_entry(avc, &anon_vma->head, same_anon_vma) {
>
>



-- 
Kind regards,
Minchan Kim
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