linux-kernel - [RFC v2 05/34] mm, slub: remove redundant unfreeze_partials() from put_cpu

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Message-Id: <20210609113903.1421-6-vbabka@suse.cz>
Date:   Wed,  9 Jun 2021 13:38:34 +0200
From:   Vlastimil Babka <vbabka@...e.cz>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Christoph Lameter <cl@...ux.com>,
        David Rientjes <rientjes@...gle.com>,
        Pekka Enberg <penberg@...nel.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Jann Horn <jannh@...gle.com>, Vlastimil Babka <vbabka@...e.cz>
Subject: [RFC v2 05/34] mm, slub: remove redundant unfreeze_partials() from put_cpu_partial()

Commit d6e0b7fa1186 ("slub: make dead caches discard free slabs immediately")
introduced cpu partial flushing for kmemcg caches, based on setting the target
cpu_partial to 0 and adding a flushing check in put_cpu_partial().
This code that sets cpu_partial to 0 was later moved by c9fc586403e7 ("slab:
introduce __kmemcg_cache_deactivate()") and ultimately removed by 9855609bde03
("mm: memcg/slab: use a single set of kmem_caches for all accounted
allocations"). However the check and flush in put_cpu_partial() was never
removed, although it's effectively a dead code. So this patch removes it.

Note that d6e0b7fa1186 also added preempt_disable()/enable() to
unfreeze_partials() which could be thus also considered unnecessary. But
further patches will rely on it, so keep it.

Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
---
 mm/slub.c | 7 -------
 1 file changed, 7 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 2953f6e43cae..f740598696b4 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2420,13 +2420,6 @@ static void put_cpu_partial(struct kmem_cache *s, struct page *page, int drain)

 	} while (this_cpu_cmpxchg(s->cpu_slab->partial, oldpage, page)
 								!= oldpage);
-	if (unlikely(!slub_cpu_partial(s))) {
-		unsigned long flags;
-
-		local_irq_save(flags);
-		unfreeze_partials(s, this_cpu_ptr(s->cpu_slab));
-		local_irq_restore(flags);
-	}
 	preempt_enable();
 #endif	/* CONFIG_SLUB_CPU_PARTIAL */
 }
-- 
2.31.1