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Sun, 7 Dec 2025 17:11:17 +0000 (UTC) Received: from dovecot-director2.suse.de ([2a07:de40:b281:106:10:150:64:167]) by imap1.dmz-prg2.suse.org with ESMTPSA id jnbjIDW1NWlSLAAAD6G6ig (envelope-from ); Sun, 07 Dec 2025 17:11:17 +0000 Message-ID: <7ff8a5b4-1422-49fc-b35e-958f1ea561c5@suse.cz> Date: Sun, 7 Dec 2025 18:11:16 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH V3] mm/slab: introduce kvfree_rcu_barrier_on_cache() for cache destruction To: Harry Yoo Cc: surenb@google.com, Liam.Howlett@oracle.com, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, urezki@gmail.com, sidhartha.kumar@oracle.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, rcu@vger.kernel.org, maple-tree@lists.infradead.org, linux-modules@vger.kernel.org, mcgrof@kernel.org, petr.pavlu@suse.com, samitolvanen@google.com, atomlin@atomlin.com, lucas.demarchi@intel.com, akpm@linux-foundation.org, jonathanh@nvidia.com, stable@vger.kernel.org, Daniel Gomez References: <20251207154148.117723-1-harry.yoo@oracle.com> Content-Language: en-US From: Vlastimil Babka Autocrypt: addr=vbabka@suse.cz; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: A54C3180012 X-Stat-Signature: tkxxwh3ya1cx3hdzo8wfehenp1f554ik X-Rspam-User: X-HE-Tag: 1765127480-732968 X-HE-Meta: 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 ePuSL7o/ oKRmeee8P476XrTr4OBG9wr5Cww/Do/W3H9uJMT4s64cjbgNKdRI5nS3l2g7DDM491GC6p6zVP1VMlW0O2vUZKTFQL2tl3Z+WoUypJLbJxvQC9YB3Ag2hssxl5KTlTudM6B02rRTppwzidNh7D9NH51ZShv9YlyASJktHPvxHvuT1CEpmqp1OXeK2MLIAlYBudCb3VEA5ETiKlM6ShFvKrjj4ZCWp2LHq4KjEoPivRafqyVym1ynNykwB9B179DgMPrZoRFKApviWM0bFfpzNGOllHW2NGgkTiN7yeACEpXSjdwfFZuuqy1qmfUbnRfhbp31GlLnAYwi3tKAHicXpdHcaVuUd1NGJJieig66BEsc9yep8fyUQiB8nkiQZmrDMUnOL07TsyuS/UM4JNzTvdA7z59E8mA8EkVLs0n7JN3kHQ5c= 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: List-Subscribe: List-Unsubscribe: On 12/7/25 16:41, Harry Yoo wrote: > Currently, kvfree_rcu_barrier() flushes RCU sheaves across all slab > caches when a cache is destroyed. This is unnecessary; only the RCU > sheaves belonging to the cache being destroyed need to be flushed. > > As suggested by Vlastimil Babka, introduce a weaker form of > kvfree_rcu_barrier() that operates on a specific slab cache. > > Factor out flush_rcu_sheaves_on_cache() from flush_all_rcu_sheaves() and > call it from flush_all_rcu_sheaves() and kvfree_rcu_barrier_on_cache(). > > Call kvfree_rcu_barrier_on_cache() instead of kvfree_rcu_barrier() on > cache destruction. > > The performance benefit is evaluated on a 12 core 24 threads AMD Ryzen > 5900X machine (1 socket), by loading slub_kunit module. > > Before: > Total calls: 19 > Average latency (us): 18127 > Total time (us): 344414 > > After: > Total calls: 19 > Average latency (us): 10066 > Total time (us): 191264 > > Two performance regression have been reported: > - stress module loader test's runtime increases by 50-60% (Daniel) > - internal graphics test's runtime on Tegra23 increases by 35% (Jon) > > They are fixed by this change. > > Suggested-by: Vlastimil Babka > Fixes: ec66e0d59952 ("slab: add sheaf support for batching kfree_rcu() operations") > Cc: > Link: https://lore.kernel.org/linux-mm/1bda09da-93be-4737-aef0-d47f8c5c9301@suse.cz > Reported-and-tested-by: Daniel Gomez > Closes: https://lore.kernel.org/linux-mm/0406562e-2066-4cf8-9902-b2b0616dd742@kernel.org > Reported-and-tested-by: Jon Hunter > Closes: https://lore.kernel.org/linux-mm/e988eff6-1287-425e-a06c-805af5bbf262@nvidia.com > Signed-off-by: Harry Yoo > --- > > v2 -> v3: > - Addressed Suren's comment [1], thanks! Thanks, replaced.