linux-kernel - Re: [PATCH] mm: zram: amend SLAB_RECLAIM_ACCOUNT on zspage

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Message-ID: <YNJ0gBerIy3k+l7H@google.com>
Date:   Tue, 22 Jun 2021 16:38:40 -0700
From:   Minchan Kim <minchan@...nel.org>
To:     Zhaoyang Huang <huangzhaoyang@...il.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Zhaoyang Huang <zhaoyang.huang@...soc.com>,
        "open list:MEMORY MANAGEMENT" <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Nitin Gupta <ngupta@...are.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH] mm: zram: amend SLAB_RECLAIM_ACCOUNT on zspage_cachep

On Mon, Jun 21, 2021 at 10:35:26AM +0800, Zhaoyang Huang wrote:
> On Sat, Jun 19, 2021 at 6:02 AM Minchan Kim <minchan@...nel.org> wrote:
> >
> > On Tue, Jun 08, 2021 at 03:28:17PM +0800, Huangzhaoyang wrote:
> > > From: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > >
> > > Zspage_cachep is found be merged with other kmem cache during test, which
> > > is not good for debug things(zs_pool->zspage_cachep present to be another
> > > kmem cache in memory dumpfile). It is also neccessary to do so as shrinker has
> >
> > It's not a only problem of zsmalloc because slab want to minimize
> > fragmentation so try to merge several objects if it's allowed.
> > So I don't think it's particular problem of zsmalloc.
> > I guess slub has some option maybe "nomerge" if you want it.
> 
> >
> > > been registered for zspage. Amending this flag can help kernel to calculate
> > > SLAB_RECLAIMBLE correctly.
> > >
> > > Signed-off-by: Zhaoyang Huang <zhaoyang.huang@...soc.com>
> > > ---
> > >  mm/zsmalloc.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> > > index 19b563b..0b0addd 100644
> > > --- a/mm/zsmalloc.c
> > > +++ b/mm/zsmalloc.c
> > > @@ -328,7 +328,7 @@ static int create_cache(struct zs_pool *pool)
> > >               return 1;
> > >
> > >       pool->zspage_cachep = kmem_cache_create("zspage", sizeof(struct zspage),
> > > -                                     0, 0, NULL);
> > > +                                     0, SLAB_RECLAIM_ACCOUNT, NULL);
> >
> > How does zspage become SLAB_RECLAIM_ACCOUNT?
> >
> > I took the flag as "cacheable" object. IOW, when the shrinker
> > ask to reclaim the object, it should reclaim(e.g., discarding)
> > those objects for reclaming. However, that's not the case
> > in zsmalloc.
> alloc_slab will take the allocated object into account as
> SLAB_RECLAIMABLE when this flag set on the kmem_cache

My point is zspage_cachep is not an reclimable slab cache.
Please describe why you believe it's reclaimable slab.