linux-kernel - Re: [PATCH v14 15/20] mm/swap: serialize memcg changes during pagevec_lru_move

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Message-ID: <20200704133330.GP25523@casper.infradead.org>
Date:   Sat, 4 Jul 2020 14:33:30 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Alex Shi <alex.shi@...ux.alibaba.com>
Cc:     Konstantin Khlebnikov <koct9i@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Tejun Heo <tj@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Константин Хлебников 
        <khlebnikov@...dex-team.ru>, daniel.m.jordan@...cle.com,
        yang.shi@...ux.alibaba.com, Johannes Weiner <hannes@...xchg.org>,
        lkp@...el.com, linux-mm@...ck.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Cgroups <cgroups@...r.kernel.org>, shakeelb@...gle.com,
        Joonsoo Kim <iamjoonsoo.kim@....com>, richard.weiyang@...il.com
Subject: Re: [PATCH v14 15/20] mm/swap: serialize memcg changes during
 pagevec_lru_move_fn

On Sat, Jul 04, 2020 at 09:12:46PM +0800, Alex Shi wrote:
> 在 2020/7/4 下午7:39, Matthew Wilcox 写道:
> > On Sat, Jul 04, 2020 at 07:34:59PM +0800, Alex Shi wrote:
> >> That's a great idea! Guess what the new struct we need would be like this?
> >> I like to try this. :)
> >>
> >>
> >> diff --git a/include/linux/pagevec.h b/include/linux/pagevec.h
> >> index 081d934eda64..d62778c8c184 100644
> >> --- a/include/linux/pagevec.h
> >> +++ b/include/linux/pagevec.h
> >> @@ -20,7 +20,7 @@
> >>  struct pagevec {
> >>         unsigned char nr;
> >>         bool percpu_pvec_drained;
> >> -       struct page *pages[PAGEVEC_SIZE];
> >> +       struct list_head veclist;
> >>  };
> > 
> > pagevecs are used not just for LRU.  If you want to use a list_head for
> > LRU then define a new structure.
> 
> yes, there are much page don't use page->lru, like slab etc. we need a new struct.

That's not what I mean.  Slab pages aren't on the LRU anyway.

Consider the callers of page_cache_delete_batch().  These use a pagevec
for a non-LRU purpose, and they will be much slower with a list_head than
with an array.