linux-kernel - Re: [RFC PATCH] mm: check global free_list if there is ongoing reclaiming when pcp fail

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Message-ID: <CAGWkznF2VvT=3sj3w8TC4JJ4XN0Y+CLGg_AYxxc4iuuVR518PQ@mail.gmail.com>
Date:   Tue, 20 Sep 2022 16:48:53 +0800
From:   Zhaoyang Huang <huangzhaoyang@...il.com>
To:     Mel Gorman <mgorman@...hsingularity.net>
Cc:     "zhaoyang.huang" <zhaoyang.huang@...soc.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>, Ke Wang <ke.wang@...soc.com>
Subject: Re: [RFC PATCH] mm: check global free_list if there is ongoing
 reclaiming when pcp fail

On Tue, Sep 20, 2022 at 4:46 PM Mel Gorman <mgorman@...hsingularity.net> wrote:
>
> On Tue, Sep 20, 2022 at 09:45:35AM +0800, Zhaoyang Huang wrote:
> > On Mon, Sep 19, 2022 at 6:22 PM Mel Gorman <mgorman@...hsingularity.net> wrote:
> > >
> > > On Fri, Sep 16, 2022 at 06:58:12PM +0800, zhaoyang.huang wrote:
> > > > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > > >
> > > > Check the global free list again even if rmqueue_bulk failed for pcp pages when
> > > > there is ongoing reclaiming, which could eliminate potential direct reclaim by
> > > > chance.
> > > >
> > > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > >
> > > Patch does not apply and may be based on a custom kernel that introduced
> > > a problem. There is no description of what problem this is trying to
> > > fix. Checking the status of reclaim for a specific zone in this path would
> > > be a little unexpected.  If allocation pressure is exceeding the ability
> > > of reclaim to make progress then the caller likely needs to take action
> > > like direct reclaim. If the allocation failure is due to a high-order
> > > failure then it may need to enter direct compaction etc.
> >
> > Agree with the above comment. This is a proposal aiming at avoiding
> > direct reclaiming things with minimum cost, that is to say, about 5
> > CPU instructions in return with the overhead of function calls which
> > has both of several loops inside and potential throttle sleep by IO
> > congestion etc.
>
> If the refill fails and kswapd is failing to keep up then actions like
> direct reclaim or compaction are inevitable. At best, this patch would
> race to allocate pages in one context that are being freed in parallel by
> another context.
>
> Nak.
ok, I have noticed that the latest modification has made some changes
on this path. thanks for comment
>
> --
> Mel Gorman
> SUSE Labs