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From: Roman Gushchin To: David Rientjes Cc: Julian Pidancet , Christoph Lameter , Pekka Enberg , Joonsoo Kim , Andrew Morton , Vlastimil Babka , Hyeonggon Yoo <42.hyeyoo@gmail.com>, linux-mm@kvack.org, Jonathan Corbet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, Matthew Wilcox , Kees Cook , Rafael Aquini Subject: Re: [PATCH] mm/slub: disable slab merging in the default configuration Message-ID: References: <20230627132131.214475-1-julian.pidancet@oracle.com> <48bd9819-3571-6b53-f1ad-ec013be742c0@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <48bd9819-3571-6b53-f1ad-ec013be742c0@google.com> X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: F08F9180023 X-Rspam-User: X-Rspamd-Server: rspam11 X-Stat-Signature: hc68e7tdkc16p1obidjastpd8are6bbd X-HE-Tag: 1687970710-360238 X-HE-Meta: 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 JuMiKKIX vt9eS53KxFcykSwtAVwyc8sPhVq1Ag3XW0LzXEHy7HpMaxX/lLJWnfqDY3Qj0OlL3w5e1JP8qBVdP9RoTziUhwRiIHT5nHjB/xK5sQtz7mrr50h77kANjPSAf0zEpZ2URDiWX2rRCXeSMit6bpZvdNl6KMHHtrJF4dYApLmjz46J7PppBadh8aY+hCtD3AgMz4PLt4FPFhxQA43jeHK6ZGWW3cw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Jun 27, 2023 at 12:32:15PM -0700, David Rientjes wrote: > On Tue, 27 Jun 2023, Julian Pidancet wrote: > > > Make CONFIG_SLAB_MERGE_DEFAULT default to n unless CONFIG_SLUB_TINY is > > enabled. Benefits of slab merging is limited on systems that are not > > memory constrained: the overhead is negligible and evidence of its > > effect on cache hotness is hard to come by. > > > > I don't have an objection to this, I think it makes sense. +1 I believe the overhead was much larger when we had per-memcg slab caches, but now it should be fairly small on most systems. But I wonder if we need a new flag (SLAB_MERGE?) to explicitly force merging on per-slab cache basis. I believe there are some cases when slab caches can be created in noticeable numbers and in those cases the memory footprint might be noticeable. Thanks!