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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:     Mike Galbraith <efault@gmx.de>,
        Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
        Thomas Gleixner <tglx@linutronix.de>,
        Mel Gorman <mgorman@techsingularity.net>,
        Jesper Dangaard Brouer <brouer@redhat.com>,
        Jann Horn <jannh@google.com>, Vlastimil Babka <vbabka@suse.cz>
Subject: [PATCH v3 10/35] mm, slub: restructure new page checks in ___slab_alloc()
Date:   Thu, 29 Jul 2021 15:21:07 +0200
Message-Id: <20210729132132.19691-11-vbabka@suse.cz>
In-Reply-To: <20210729132132.19691-1-vbabka@suse.cz>
References: <20210729132132.19691-1-vbabka@suse.cz>
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When we allocate slab object from a newly acquired page (from node's partial
list or page allocator), we usually also retain the page as a new percpu slab.
There are two exceptions - when pfmemalloc status of the page doesn't match our
gfp flags, or when the cache has debugging enabled.

The current code for these decisions is not easy to follow, so restructure it
and add comments. The new structure will also help with the following changes.
No functional change.

Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/slub.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 92a866adce3d..469aa8155663 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2765,13 +2765,29 @@ static void *___slab_alloc(struct kmem_cache *s, gfp_t gfpflags, int node,
 	c->page = page;
 
 check_new_page:
-	if (likely(!kmem_cache_debug(s) && pfmemalloc_match(page, gfpflags)))
-		goto load_freelist;
 
-	/* Only entered in the debug case */
-	if (kmem_cache_debug(s) &&
-			!alloc_debug_processing(s, page, freelist, addr))
-		goto new_slab;	/* Slab failed checks. Next slab needed */
+	if (kmem_cache_debug(s)) {
+		if (!alloc_debug_processing(s, page, freelist, addr))
+			/* Slab failed checks. Next slab needed */
+			goto new_slab;
+		else
+			/*
+			 * For debug case, we don't load freelist so that all
+			 * allocations go through alloc_debug_processing()
+			 */
+			goto return_single;
+	}
+
+	if (unlikely(!pfmemalloc_match(page, gfpflags)))
+		/*
+		 * For !pfmemalloc_match() case we don't load freelist so that
+		 * we don't make further mismatched allocations easier.
+		 */
+		goto return_single;
+
+	goto load_freelist;
+
+return_single:
 
 	deactivate_slab(s, page, get_freepointer(s, freelist), c);
 	return freelist;
-- 
2.32.0