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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 15/26] mm, slub: stop disabling irqs around get_partial()
Date:   Tue, 25 May 2021 01:39:35 +0200
Message-Id: <20210524233946.20352-16-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 get_partial() does not need to have irqs disabled as a whole. It's
sufficient to convert spin_lock operations to their irq saving/restoring
versions.

As a result, it's now possible to reach the page allocator from the slab
allocator without disabling and re-enabling interrupts on the way.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
 mm/slub.c | 20 ++++++++------------
 1 file changed, 8 insertions(+), 12 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index e092387b5932..bc7bee5d4bf2 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1964,11 +1964,12 @@ static inline bool pfmemalloc_match(struct page *page, gfp_t gfpflags);
  * Try to allocate a partial slab from a specific node.
  */
 static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
-			      struct page **ret_page, gfp_t flags)
+			      struct page **ret_page, gfp_t gfpflags)
 {
 	struct page *page, *page2;
 	void *object = NULL;
 	unsigned int available = 0;
+	unsigned long flags;
 	int objects;
 
 	/*
@@ -1980,11 +1981,11 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 	if (!n || !n->nr_partial)
 		return NULL;
 
-	spin_lock(&n->list_lock);
+	spin_lock_irqsave(&n->list_lock, flags);
 	list_for_each_entry_safe(page, page2, &n->partial, slab_list) {
 		void *t;
 
-		if (!pfmemalloc_match(page, flags))
+		if (!pfmemalloc_match(page, gfpflags))
 			continue;
 
 		t = acquire_slab(s, n, page, object == NULL, &objects);
@@ -2005,7 +2006,7 @@ static void *get_partial_node(struct kmem_cache *s, struct kmem_cache_node *n,
 			break;
 
 	}
-	spin_unlock(&n->list_lock);
+	spin_unlock_irqrestore(&n->list_lock, flags);
 	return object;
 }
 
@@ -2722,8 +2723,10 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 			local_irq_restore(flags);
 			goto reread_page;
 		}
-		if (unlikely(!slub_percpu_partial(c))) /* stolen by IRQ? */
+		if (unlikely(!slub_percpu_partial(c))) { /* stolen by IRQ? */
+			local_irq_restore(flags);
 			goto new_objects;
+		}
 
 		page = c->page = slub_percpu_partial(c);
 		slub_set_percpu_partial(c, page);
@@ -2732,16 +2735,9 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 		goto redo;
 	}
 
-	local_irq_save(flags);
-	if (unlikely(c->page)) {
-		local_irq_restore(flags);
-		goto reread_page;
-	}
-
 new_objects:
 
 	freelist = get_partial(s, gfpflags, node, &page);
-	local_irq_restore(flags);
 	if (freelist)
 		goto check_new_page;
 
-- 
2.31.1