linux-kernel - Re: [PATCH] mm, compaction: fast_find_migrateblock() should return pfn in the target zone

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Message-Id: <20220511192000.d4851d55c5560e720e1e2914@linux-foundation.org>
Date:   Wed, 11 May 2022 19:20:00 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Rei Yamamoto <yamamoto.rei@...fujitsu.com>
Cc:     linmiaohe@...wei.com, aquini@...hat.com, ddutile@...hat.com,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        mgorman@...hsingularity.net, vvghjk1234@...il.com
Subject: Re: [PATCH] mm, compaction: fast_find_migrateblock() should return
 pfn in the target zone

On Thu, 12 May 2022 10:47:36 +0900 Rei Yamamoto <yamamoto.rei@...fujitsu.com> wrote:

> ...
>
> > Sorry, I think you're right. And could you please add the runtime effect of this issue?
> >
> > Anyway, this patch looks good to me now. Thanks!
> 
> Thank you for your review.
> The runtime effect is that compaction become unintended behavior.
> For example, pages not in the target zone are added to cc->migratepages list in isolate_migratepages_block().
> As a result, pages migrate between nodes unintentionally.

Thanks.   I updated the changelog thusly:

: At present, pages not in the target zone are added to cc->migratepages
: list in isolate_migratepages_block().  As a result, pages may migrate
: between nodes unintentionally.
: 
: Avoid returning a pfn outside the target zone in the case that it is
: not aligned with a pageblock boundary.  Otherwise
: isolate_migratepages_block() will handle pages not in the target zone.