linux-kernel - Re: [PATCH 1/2] mm/slub: wake up kswapd for initial high order allocation

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Date:   Tue, 29 Aug 2017 09:14:00 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH 1/2] mm/slub: wake up kswapd for initial high order
 allocation

On 08/29/2017 02:22 AM, Joonsoo Kim wrote:
> On Mon, Aug 28, 2017 at 12:04:41PM +0200, Vlastimil Babka wrote:
>>
>> Hm, so this seems to revert Mel's 444eb2a449ef ("mm: thp: set THP defrag
>> by default to madvise and add a stall-free defrag option") wrt the slub
>> allocate_slab() part. AFAICS the intention in Mel's patch was that he
>> removed a special case in __alloc_page_slowpath() where including
>> __GFP_THISNODE and lacking ~__GFP_DIRECT_RECLAIM effectively means also
>> lacking __GFP_KSWAPD_RECLAIM. The commit log claims that slab/slub might
>> change behavior so he moved the removal of __GFP_KSWAPD_RECLAIM to them.
>>
>> But AFAICS, only slab uses __GFP_THISNODE, while slub doesn't. So your
>> patch would indeed revert an unintentional change of Mel's commit. Is it
>> right or do I miss something?
> 
> I didn't look at that patch. What I tried here is just restoring first
> intention of this code. I now realize that Mel did it for specific
> purpose. Thanks for notifying it.
> 
> Anyway, your analysis looks correct and this change doesn't hurt Mel's
> intention and restores original behaviour of the code. I will add your
> analysis on the commit description and resubmit it. Is it okay to you?

Yeah, no problem.

> Thanks.
>