linux-kernel - Re: [PATCH] mm, page_alloc: simplify hot/cold page handling in rmqueue

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Message-ID: <d1f1fb5d-6f93-9a9b-bde1-491f4ebf29e0@suse.cz>
Date:   Wed, 18 Oct 2017 10:38:14 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>
Subject: Re: [PATCH] mm, page_alloc: simplify hot/cold page handling in
 rmqueue_bulk()

On 10/18/2017 10:06 AM, Mel Gorman wrote:
> On Wed, Oct 18, 2017 at 09:35:28AM +0200, Vlastimil Babka wrote:
>> The code for filling the pcplists in order determined by the cold flag also
>> seems unnecessarily hard to follow. It's sufficient to either use list_add()
>> or list_add_tail(), but the current code also updates the list head pointer
>> in each step to the last added page, which then counterintuitively requires
>> to switch the usage of list_add() and list_add_tail() to achieve the desired
>> order, with no apparent benefit. This patch simplifies the code.
>>
>> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> 
> The "cold" treatment is dubious because almost everything that frees
> considers the page "hot" which limits the usefulness of hot/cold in the
> allocator. While I do not see a problem with your patch as such, please
> take a look at "mm: Remove __GFP_COLD" in particular. The last 4 patches
> in that series make a number of observations on how "cold" is treated in
> the allocator.

Ah, somehow I managed to miss that series, thanks for pointing me.