Re: [PATCH] mm: zram: amend SLAB_RECLAIM_ACCOUNT on zspage_cachep

[Zhaoyang Huang]

On Sat, Jun 19, 2021 at 6:02 AM Minchan Kim <minchan@xxxxxxxxxx> wrote:
>
> On Tue, Jun 08, 2021 at 03:28:17PM +0800, Huangzhaoyang wrote:
> > From: Zhaoyang Huang <zhaoyang.huang@xxxxxxxxxx>
> >
> > 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@xxxxxxxxxx>
> > ---
> >  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