linux-kernel - Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE

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Message-ID: <20170224233752.GB4635@bbox>
Date:   Sat, 25 Feb 2017 08:37:52 +0900
From:   Minchan Kim <minchan@...nel.org>
To:     Shaohua Li <shli@...com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Kernel-team@...com, mhocko@...e.com, hughd@...gle.com,
        hannes@...xchg.org, riel@...hat.com, mgorman@...hsingularity.net,
        akpm@...ux-foundation.org
Subject: Re: [PATCH V4 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE
 list

Hi Shaohua,

On Thu, Feb 23, 2017 at 10:15:50PM -0800, Shaohua Li wrote:
> On Fri, Feb 24, 2017 at 10:49:39AM +0900, Minchan Kim wrote:
> > On Wed, Feb 22, 2017 at 10:50:41AM -0800, Shaohua Li wrote:
> > > madv MADV_FREE indicate pages are 'lazyfree'. They are still anonymous
> > > pages, but they can be freed without pageout. To destinguish them
> > > against normal anonymous pages, we clear their SwapBacked flag.
> > > 
> > > MADV_FREE pages could be freed without pageout, so they pretty much like
> > > used once file pages. For such pages, we'd like to reclaim them once
> > > there is memory pressure. Also it might be unfair reclaiming MADV_FREE
> > > pages always before used once file pages and we definitively want to
> > > reclaim the pages before other anonymous and file pages.
> > > 
> > > To speed up MADV_FREE pages reclaim, we put the pages into
> > > LRU_INACTIVE_FILE list. The rationale is LRU_INACTIVE_FILE list is tiny
> > > nowadays and should be full of used once file pages. Reclaiming
> > > MADV_FREE pages will not have much interfere of anonymous and active
> > > file pages. And the inactive file pages and MADV_FREE pages will be
> > > reclaimed according to their age, so we don't reclaim too many MADV_FREE
> > > pages too. Putting the MADV_FREE pages into LRU_INACTIVE_FILE_LIST also
> > > means we can reclaim the pages without swap support. This idea is
> > > suggested by Johannes.
> > > 
> > > This patch doesn't move MADV_FREE pages to LRU_INACTIVE_FILE list yet to
> > > avoid bisect failure, next patch will do it.
> > > 
> > > The patch is based on Minchan's original patch.
> > > 
> > > Cc: Michal Hocko <mhocko@...e.com>
> > > Cc: Minchan Kim <minchan@...nel.org>
> > > Cc: Hugh Dickins <hughd@...gle.com>
> > > Cc: Rik van Riel <riel@...hat.com>
> > > Cc: Mel Gorman <mgorman@...hsingularity.net>
> > > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > > Suggested-by: Johannes Weiner <hannes@...xchg.org>
> > > Signed-off-by: Shaohua Li <shli@...com>
> > 
> > Other than that Johannes pointed out, code itself looks good to me.
> > However, I hope to merge this patch with next one.
> > It's enough simple to merge, change behavior(about deactivation),
> > mark_page_lazyfree is introduced but there is no callsite to use it
> > in this patch.
> > 
> > I don't think it's worth to separate.
> 
> I think it's more clear in this way, doing one thing in one patch.

There are several times to prevent it that introduce new function
*here* and use it *there*. One of example from Johannes:

https://marc.info/?l=linux-mm&m=147430500910960&w=2

I don't understand why this case is okay.
Nomally, it's anti-pattern for git-bisect which adds uselss bisect
point. Even, if it were good for review, I might agree but this
case is not that, too.