[RFC PATCH 5/5] mm, slub: make reclaim_account attribute read-only

From: Vlastimil Babka <vbabka@suse.cz>
To: Christoph Lameter <cl@linux.com>,
	Pekka Enberg <penberg@kernel.org>,
	David Rientjes <rientjes@google.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	kernel-team@android.com, vinmenon@codeaurora.org,
	Kees Cook <keescook@chromium.org>,
	Matthew Garrett <mjg59@google.com>,
	Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
	Vijayanand Jitta <vjitta@codeaurora.org>
Subject: [RFC PATCH 5/5] mm, slub: make reclaim_account attribute read-only
Date: Tue,  2 Jun 2020 16:15:19 +0200	[thread overview]
Message-ID: <20200602141519.7099-6-vbabka@suse.cz> (raw)
In-Reply-To: <20200602141519.7099-1-vbabka@suse.cz>

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@suse.cz>
---
 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

