linux-kernel - Re: [PATCH] mm: avoid blocking lock

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Date:   Tue, 28 Jan 2020 11:44:47 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Matthew Wilcox <willy@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-mm <linux-mm@...ck.org>, Mel Gorman <mgorman@...e.de>,
        Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH] mm: avoid blocking lock_page() in kcompactd

On Tue, Jan 28, 2020 at 3:39 AM Michal Hocko <mhocko@...nel.org> wrote:
>
> On Tue 28-01-20 02:48:57, Matthew Wilcox wrote:
> > Doesn't the stack trace above indicate that we're doing migration as
> > the result of an allocation in add_to_page_cache_lru()?
>
> Which stack trace do you refer to? Because the one above doesn't show
> much more beyond mem_cgroup_iter and likewise others in this email
> thread. I do not really remember any stack with lock_page on the trace.

I think the page is locked in add_to_page_cache_lru() by
__SetPageLocked(), as the stack trace shows __add_to_page_cache_locked().
It is not yet unlocked, as it is still looping inside try_charge().

I will write a script to see if I can find the longest time spent in reclaim
as you suggested.

Thanks.