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

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Message-ID: <CAGWkznFEBDwDVeR1AH6gk30PHU3pvSHBusOSQgEB2L7mZD4Mxg@mail.gmail.com>
Date:   Tue, 20 Sep 2022 09:45:35 +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 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.
>
> --
> Mel Gorman
> SUSE Labs