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From:   Vlastimil Babka <vbabka@suse.cz>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Christoph Lameter <cl@linux.com>,
        David Rientjes <rientjes@google.com>,
        Pekka Enberg <penberg@kernel.org>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mel Gorman <mgorman@techsingularity.net>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Jann Horn <jannh@google.com>, Vlastimil Babka <vbabka@suse.cz>
Subject: [RFC 18/26] mm, slub: call deactivate_slab() without disabling irqs
Date:   Tue, 25 May 2021 01:39:38 +0200
Message-Id: <20210524233946.20352-19-vbabka@suse.cz>
In-Reply-To: <20210524233946.20352-1-vbabka@suse.cz>
References: <20210524233946.20352-1-vbabka@suse.cz>
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The function is now safe to be called with irqs enabled, so move the calls
outside of irq disabled sections.

When called from ___slab_alloc() -> flush_slab() we have irqs disabled, so to
reenable them before deactivate_slab() we need to open-code flush_slab() in
___slab_alloc() and reenable irqs after modifying the kmem_cache_cpu fields.
But that means another irq might have assigned a new c->page so we have to
retry the whole check.

The remaining callers of flush_slab() are the IPI handler which has disabled
irqs anyway, and slub_cpu_dead() which will be dealt with in the following
patch.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/slub.c | 23 ++++++++++++++++++-----
 1 file changed, 18 insertions(+), 5 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 0f58859165bf..01422c757f9b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2722,8 +2722,8 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	freelist = c->freelist;
 	c->page = NULL;
 	c->freelist = NULL;
-	deactivate_slab(s, page, freelist);
 	local_irq_restore(flags);
+	deactivate_slab(s, page, freelist);
 
 new_slab:
 
@@ -2792,18 +2792,31 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		 */
 		goto return_single;
 
+retry_load_page:
 	local_irq_save(flags);
-	if (unlikely(c->page))
-		flush_slab(s, c);
+	if (unlikely(c->page)) {
+		void *flush_freelist = c->freelist;
+		struct page *flush_page = c->page;
+
+		c->page = NULL;
+		c->freelist = NULL;
+		c->tid = next_tid(c->tid);
+
+		local_irq_restore(flags);
+
+		deactivate_slab(s, flush_page, flush_freelist);
+
+		stat(s, CPUSLAB_FLUSH);
+
+		goto retry_load_page;
+	}
 	c->page = page;
 
 	goto load_freelist;
 
 return_single:
 
-	local_irq_save(flags);
 	deactivate_slab(s, page, get_freepointer(s, freelist));
-	local_irq_restore(flags);
 	return freelist;
 }
 
-- 
2.31.1