linux-kernel - Re: [RFC][PATCH] lru_add_drain_all() don't use schedule_on_each

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Message-ID: <2f11576a0810290017g310e4469gd27aa857866849bd@mail.gmail.com>
Date:	Wed, 29 Oct 2008 16:17:19 +0900
From:	"KOSAKI Motohiro" <kosaki.motohiro@...fujitsu.com>
To:	"Lee Schermerhorn" <Lee.Schermerhorn@...com>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Christoph Lameter" <cl@...ux-foundation.org>,
	heiko.carstens@...ibm.com, npiggin@...e.de,
	linux-kernel@...r.kernel.org, hugh@...itas.com,
	torvalds@...ux-foundation.org, riel@...hat.com, linux-mm@...ck.org
Subject: Re: [RFC][PATCH] lru_add_drain_all() don't use schedule_on_each_cpu()

> I believe that we still  have the lru_drain_all() called from the fault
> path [with mmap_sem held] in clear_page_mlock().  We call
> clear_page_mlock() on COW of an mlocked page in a VM_LOCKED vma to
> ensure that we don't end up with an mlocked page in some other task's
> non-VM_LOCKED vma where we'd then fail to munlock it later.  During
> development testing, Rik encountered scenarios where a page would
> encounter a COW fault while it was still making its way to the LRU via
> the pagevecs.  So, he added the 'drain_all() and that seemed to avoid
> this scenario.

Agreed.


> Now, in the current upstream version of the unevictable mlocked pages
> patches, we just count any mlocked pages [vmstat] that make their way to
> free*page() instead of BUGging out, as we were doing earlier during
> development.  So, maybe we can drop the lru_drain_add()s in the
> unevictable mlocked pages work and live with the occasional freed
> mlocked page, or mlocked page on the active/inactive lists to be dealt
> with by vmscan.

hm, okey.
maybe, I was wrong.

I'll make "dropping lru_add_drain_all()" patch soon.
I expect I need few days.
  make the patch:                  1 day
  confirm by stress workload:  2-3 days

because rik's original problem only happend on heavy wokload, I think.
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