linux-kernel - Re: [RFC PATCH 5/5] mm, slub: make reclaim

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Date:   Fri, 5 Jun 2020 17:34:11 -0700
From:   Roman Gushchin <guro@...com>
To:     Vlastimil Babka <vbabka@...e.cz>
CC:     Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <kernel-team@...roid.com>,
        <vinmenon@...eaurora.org>, Kees Cook <keescook@...omium.org>,
        Matthew Garrett <mjg59@...gle.com>,
        Jann Horn <jannh@...gle.com>,
        Vijayanand Jitta <vjitta@...eaurora.org>
Subject: Re: [RFC PATCH 5/5] mm, slub: make reclaim_account attribute
 read-only

On Tue, Jun 02, 2020 at 04:15:19PM +0200, Vlastimil Babka wrote:
> The attribute reflects the SLAB_RECLAIM_ACCOUNT cache flag. It's not clear why
> this attribute was writable in the first place, as it's tied to how the cache
> is used by its creator, it's not a user tunable. Furthermore:
> 
> - it affects slab merging, but that's not being checked while toggled
> - if affects whether __GFP_RECLAIMABLE flag is used to allocate page, but
>   the runtime toggle doesn't update allocflags
> - it affects cache_vmstat_idx() so runtime toggle might lead to incosistency
>   of NR_SLAB_RECLAIMABLE and NR_SLAB_UNRECLAIMABLE
> 
> Thus make it read-only.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>

Acked-by: Roman Gushchin <guro@...com>

> ---
>  mm/slub.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/mm/slub.c b/mm/slub.c
> index 38dd6f3ebb04..d4a9a097da50 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -5223,16 +5223,7 @@ static ssize_t reclaim_account_show(struct kmem_cache *s, char *buf)
>  {
>  	return sprintf(buf, "%d\n", !!(s->flags & SLAB_RECLAIM_ACCOUNT));
>  }
> -
> -static ssize_t reclaim_account_store(struct kmem_cache *s,
> -				const char *buf, size_t length)
> -{
> -	s->flags &= ~SLAB_RECLAIM_ACCOUNT;
> -	if (buf[0] == '1')
> -		s->flags |= SLAB_RECLAIM_ACCOUNT;
> -	return length;
> -}
> -SLAB_ATTR(reclaim_account);
> +SLAB_ATTR_RO(reclaim_account);
>  
>  static ssize_t hwcache_align_show(struct kmem_cache *s, char *buf)
>  {
> -- 
> 2.26.2
> 
>