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

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Message-ID: <202006051407.2B00B067@keescook>
Date:   Fri, 5 Jun 2020 14:07:26 -0700
From:   Kees Cook <keescook@...omium.org>
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, 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>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook