linux-kernel - [PATCH 5/9] mm, slub: make reclaim

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Date:   Wed, 10 Jun 2020 18:31:31 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     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>,
        Roman Gushchin <guro@...com>, Vlastimil Babka <vbabka@...e.cz>,
        Jann Horn <jannh@...gle.com>,
        Vijayanand Jitta <vjitta@...eaurora.org>
Subject: [PATCH 5/9] mm, slub: make reclaim_account attribute read-only

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 toggling 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>
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 0108829838e7..8dd2925448ae 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