From: Vlastimil Babka <vbabka@suse.cz>
To: Andrew Morton <akpm@linux-foundation.org>,
David Rientjes <rientjes@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [patch] mm, compaction: properly initialize alloc_flags in compact_control
Date: Tue, 17 Oct 2017 08:51:07 +0200 [thread overview]
Message-ID: <cf51bc1a-8e12-8c91-3012-238a65ce1c55@suse.cz> (raw)
In-Reply-To: <20171016151252.ee4cc68f7e022bab447478d4@linux-foundation.org>
On 10/17/2017 12:12 AM, Andrew Morton wrote:
> On Mon, 16 Oct 2017 15:03:37 -0700 (PDT) David Rientjes <rientjes@google.com> wrote:
>
>>
>> compaction_suitable() requires a useful cc->alloc_flags, otherwise the
>> results of compact_zone() can be indeterminate. Kcompactd currently
>> checks compaction_suitable() itself with alloc_flags == 0, but passes an
>> uninitialized value from the stack to compact_zone(), which does its own
>> check.
>>
>> The same is true for compact_node() when explicitly triggering full node
>> compaction.
>>
>> Properly initialize cc.alloc_flags on the stack.
>>
>
> The compiler will zero any not-explicitly-initialized fields in these
> initializers.
Right.
>> @@ -1945,8 +1947,8 @@ static void kcompactd_do_work(pg_data_t *pgdat)
>> if (compaction_deferred(zone, cc.order))
>> continue;
>>
>> - if (compaction_suitable(zone, cc.order, 0, zoneid) !=
>> - COMPACT_CONTINUE)
>> + if (compaction_suitable(zone, cc.order, cc.alloc_flags,
>> + zoneid) != COMPACT_CONTINUE)
>> continue;
>
> So afaict the above hunk is the only functional change here. It will
> propagate any of compact_zone()'s modifications to cc->alloc_flags into
> succeeding calls to compaction_suitable(). I suspect this is a
> no-op (didn't look), and it wasn't changelogged.
compact_zone() shouldn't modify cc->alloc_flags. Actually, it's even
declared as "const" in struct compact_control.
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prev parent reply other threads:[~2017-10-17 6:51 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-16 22:03 David Rientjes
2017-10-16 22:12 ` Andrew Morton
2017-10-17 6:51 ` Vlastimil Babka [this message]
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