linux-kernel - Re: [RFC][PATCH 1/2] mm: use MIGRATE

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Message-ID: <20170307112953.GF28642@dhcp22.suse.cz>
Date:   Tue, 7 Mar 2017 12:29:53 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Xishi Qiu <qiuxishi@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Minchan Kim <minchan@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Yisheng Xie <xieyisheng1@...wei.com>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 1/2] mm: use MIGRATE_HIGHATOMIC as late as possible

On Tue 07-03-17 19:03:39, Xishi Qiu wrote:
> On 2017/3/7 18:47, Michal Hocko wrote:
> 
> > On Tue 07-03-17 18:33:53, Xishi Qiu wrote:
> >> MIGRATE_HIGHATOMIC page blocks are reserved for an atomic
> >> high-order allocation, so use it as late as possible.
> > 
> > Why is this better? Are you seeing any problem which this patch
> > resolves? In other words the patch description should explain why not
> > only what (that is usually clear from looking at the diff).
> > 
> 
> Hi Michal,
> 
> I have not see any problem yet, I think if we reserve more high order
> pageblocks, the more success rate we will get when meet an atomic
> high-order allocation, right?

Please make sure you measure your changes under different workloads and
present numbers in the changelog when you are touch such a subtle things
like memory reserves. Ideas that might sound they make sense can turn
out to behave differently in the real life.
-- 
Michal Hocko
SUSE Labs