linux-kernel - Re: [PATCH V5 3/6] mm: move MADV_FREE pages into LRU_INACTIVE

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Date:   Mon, 27 Feb 2017 08:13:10 -0800
From:   Shaohua Li <shli@...com>
To:     Minchan Kim <minchan@...nel.org>
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 V5 3/6] mm: move MADV_FREE pages into LRU_INACTIVE_FILE
 list

On Mon, Feb 27, 2017 at 03:28:01PM +0900, Minchan Kim wrote:
> Hello Shaohua,
> 
> On Fri, Feb 24, 2017 at 01:31:46PM -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>
> 
> This patch doesn't address I pointed out in v4.
> 
> https://marc.info/?i=20170224233752.GB4635%40bbox
> 
> Let's discuss it if you still are against.

I really think a spearate patch makes the code clearer. There are a lot of
places we introduce a function but don't use it immediately, if the way makes
the code clearer. But anyway, I'll let Andrew decide if the two patches should
be merged.

Thanks,
Shaohua