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Tue, 09 Dec 2025 16:26:40 -0800 (PST) Received: from fedora ([2a01:7e03::f03c:91ff:fe02:b162]) by smtp.gmail.com with ESMTPSA id a92af1059eb24-11df76e2f3csm70907328c88.5.2025.12.09.16.26.34 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 09 Dec 2025 16:26:40 -0800 (PST) From: Hao Li X-Google-Original-From: Hao Li Date: Wed, 10 Dec 2025 08:26:31 +0800 To: vbabka@suse.cz, akpm@linux-foundation.org, harry.yoo@oracle.com, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, haolee.swjtu@gmail.com Cc: cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Hao Li Subject: [PATCH v2] slub: keep empty main sheaf as spare in __pcs_replace_empty_main() Message-ID: <20251210002629.34448-1-haoli.tcs@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" From: Hao Li When __pcs_replace_empty_main() fails to obtain a full sheaf directly from the barn, it may either: - Refill an empty sheaf obtained via barn_get_empty_sheaf(), or - Allocate a brand new full sheaf via alloc_full_sheaf(). After reacquiring the per-CPU lock, if pcs->main is still empty and pcs->spare is NULL, the current code donates the empty main sheaf to the barn via barn_put_empty_sheaf() and installs the full sheaf as pcs->main, leaving pcs->spare unpopulated. Instead, keep the existing empty main sheaf locally as the spare: pcs->spare =3D pcs->main; pcs->main =3D full; This populates pcs->spare earlier, which can reduce future barn traffic. Suggested-by: Vlastimil Babka Signed-off-by: Hao Li --- The Gmail account(haoli.tcs) I used to send v1 of the patch has been restricted from sending emails for unknown reasons, so I'm sending v2 from this address instead. Thanks. mm/slub.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/mm/slub.c b/mm/slub.c index a0b905c2a557..a3e73ebb0cc8 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -5077,6 +5077,11 @@ __pcs_replace_empty_main(struct kmem_cache *s, struc= t slub_percpu_sheaves *pcs, */ =20 if (pcs->main->size =3D=3D 0) { + if (!pcs->spare) { + pcs->spare =3D pcs->main; + pcs->main =3D full; + return pcs; + } barn_put_empty_sheaf(barn, pcs->main); pcs->main =3D full; return pcs; --=20 2.50.1