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h=Date:Subject:To:Cc:References:From:In-Reply-To; b=KAmVci8prSKWVWJDnnMjbYXecaey/m2kdgGlten0/MtSDBWAlDx8QxRDeBkvN21bU 45Dte5iInWRKBTstP++cGXcQNrRvBS5+5pFA8rdY/80T1Wo/lwhVk6IKJ91I/G/PmI vnX16dokZr9anglrKFOakFh6Uv2BfmfYE9NDELvBOGm/W1wrAyq2y+YdryL+mCTAU5 A7cQeUv80a1u4/TR8ixPULvU6UFLlT1rsV1s0u8GnFPEft6rYwHZiivLCJeayyktUf B8DUmSJcSqr4XH8tsArVvYzCbNBgSqd/UpxitfmykLMDSyG7/UM6tHePNDjf7ROgK/ EHim5TRRJEilA== Message-ID: <07adab0f-12cc-4f48-bf23-4aaef67ab405@kernel.org> Date: Fri, 24 Jul 2026 20:42:52 +0900 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH slab/for-next v4 4/8] mm/slab: extend deferred free mechanism to handle rcu sheaves To: hu.shengming@zte.com.cn Cc: vbabka@kernel.org, akpm@linux-foundation.org, hao.li@linux.dev, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, ast@kernel.org, andrii@kernel.org, puranjay@kernel.org, ameryhung@gmail.com, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, paulmck@kernel.org, frederic@kernel.org, neeraj.upadhyay@kernel.org, joelagnelf@nvidia.com, josh@joshtriplett.org, boqun@kernel.org, urezki@gmail.com, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang@linux.dev, pfalcato@suse.de, surenb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, rcu@vger.kernel.org, bpf@vger.kernel.org References: <20260723182727858gUQJ4TgRU2b6v1kdgpkfV@zte.com.cn> Content-Language: en-US From: Harry Yoo In-Reply-To: <20260723182727858gUQJ4TgRU2b6v1kdgpkfV@zte.com.cn> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="------------tmAUU7aaQUfp05UMAY0PS3Nq" X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 0606F1C0002 X-Stat-Signature: xyggamyx3ux6pfwpnozbus5a6mmsaiw3 X-Rspam-User: X-HE-Tag: 1784893399-16905 X-HE-Meta: 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 WNU9xl/V pGv8rlapQa1VSDafC18+Ptp7DGK+7RhiTuis579Kaq1xifyZovogU1ddtXhLd3YJrnE9rg6bH2HOXN8eFvmvPZ41GZL45X0RSrSd0OhPeJfwU/MkAMqTxwJvvcB4pIHtU2EFEFcMizJZAdc2xmLlYMOczn+yPNbBlviZqlKzkpBEVXBYfe1s040IZvcgAKxR55hluW46ANOkAirSniVGHltOuZl0HccfdHOm93VHMOJpUYKkmDGFovdeHUVe5Kohm5AIAd3N4I0corhOrmxl167oBRmMTaTfPyL0CIL/XVdTOf5PjZBh3UpqtsAEtHgyveac1awlI11qUDrkui3+/W7Jlr+J+TnibY0hHk2TIP6A9Uvdemr0M4U5odagcrCjGl903Df1YEj70BKLzKosbJxu/GwSYzGgVa2mpW0F1bofAUcSSRq3561la0wlXcH9iDlmE+zPCVxbysTX8yTsghQbdgu/NZJJEj0HG7DqyD2+WXf5bQBNmw/azYYg91uFD3gvUZmA1vk77iIFxgd59B2DyAvQTYBAnr4b0 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --------------tmAUU7aaQUfp05UMAY0PS3Nq Content-Type: multipart/mixed; boundary="------------l88ZLZ879gKaeoF6sUZa3ymK"; protected-headers="v1" From: Harry Yoo To: hu.shengming@zte.com.cn Cc: vbabka@kernel.org, akpm@linux-foundation.org, hao.li@linux.dev, cl@gentwo.org, rientjes@google.com, roman.gushchin@linux.dev, ast@kernel.org, andrii@kernel.org, puranjay@kernel.org, ameryhung@gmail.com, bigeasy@linutronix.de, clrkwllms@kernel.org, rostedt@goodmis.org, paulmck@kernel.org, frederic@kernel.org, neeraj.upadhyay@kernel.org, joelagnelf@nvidia.com, josh@joshtriplett.org, boqun@kernel.org, urezki@gmail.com, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, qiang.zhang@linux.dev, pfalcato@suse.de, surenb@google.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, rcu@vger.kernel.org, bpf@vger.kernel.org Message-ID: <07adab0f-12cc-4f48-bf23-4aaef67ab405@kernel.org> Subject: Re: [PATCH slab/for-next v4 4/8] mm/slab: extend deferred free mechanism to handle rcu sheaves References: <20260723182727858gUQJ4TgRU2b6v1kdgpkfV@zte.com.cn> In-Reply-To: <20260723182727858gUQJ4TgRU2b6v1kdgpkfV@zte.com.cn> --------------l88ZLZ879gKaeoF6sUZa3ymK Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On 7/23/26 7:27 PM, hu.shengming@zte.com.cn wrote: > Harry wrote: >> __kfree_rcu_sheaf() cannot invoke call_rcu() when spinning is not >> allowed and IRQs are disabled. To relax the limitation, extend the >> deferred free fallback so that a full rcu sheaf can be submitted to >> call_rcu() via the existing IRQ work. >> >> Since the deferred mechanism does more than deferred freeing of object= s, >> rename the struct to deferred_percpu_work and adjust names accordingly= =2E >> >> When a sheaf is queued on an IRQ work, it is detached from >> pcs->rcu_free but call_rcu() is not invoked until the irq_work runs. >> To keep the kvfree_rcu barrier's promise, call irq_work_sync() on each= >> CPU before calling rcu_barrier(). >> >> In the meantime, remove the TODO item as apparently there is no simple= >> and effective way to achieve that. This is because, unlike sheaves, >> kfree_rcu() batches objects from different caches together. >> >> Suggested-by: Alexei Starovoitov >> Reviewed-by: Pedro Falcato >> Reviewed-by: Vlastimil Babka (SUSE) >> Signed-off-by: Harry Yoo (Oracle) >> --- >> mm/slab.h | 2 +- >> mm/slab_common.c | 7 ++--- >> mm/slub.c | 85 +++++++++++++++++++++++++++++++++--------------= --------- >> 3 files changed, 53 insertions(+), 41 deletions(-) >> >> diff --git a/mm/slab_common.c b/mm/slab_common.c >> index e07b4e6d6679..9c9ae1384f47 100644 >> --- a/mm/slab_common.c >> +++ b/mm/slab_common.c >> @@ -551,7 +551,7 @@ void kmem_cache_destroy(struct kmem_cache *s) >> } >> =20 >> /* Wait for deferred work from kmalloc/kfree_nolock() */ >> - defer_free_barrier(); >> + deferred_work_barrier(); >> =20 >> cpus_read_lock(); >> mutex_lock(&slab_mutex); >=20 > Hi Harry, Hi Shengming, > I noticed that your fix in [1] serializes defer_free_barrier() to > avoid concurrent irq_work_sync() waiters. Right. > However, this patch still calls the renamed deferred_work_barrier() > outside that serialization scope, including the new call sites in > kvfree_rcu_barrier_on_cache() and flush_all_rcu_sheaves(). Good point! I didn't _fix_ that as part of this patch since that would be confusing and the fix didn't land the mainline or slab yet. > Is this series expected to depend on [1], with these call sites > moved under the same serialization? Or am I missing something? I was thinking of rebasing the fixes as there won't be much conflicts, nobody except for sashiko complained about this, and we're not going to backport them anyway. > [1] > https://lore.kernel.org/all/20260624-kmalloc-nolock-fixes-v1-4-fdf4d173= 51dd@kernel.org/ >=20 > thanks, >=20 > -- > With Best Regards, > Shengming --=20 Cheers, Harry / Hyeonggon --------------l88ZLZ879gKaeoF6sUZa3ymK-- --------------tmAUU7aaQUfp05UMAY0PS3Nq Content-Type: application/pgp-signature; name="OpenPGP_signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="OpenPGP_signature.asc" -----BEGIN PGP SIGNATURE----- iHUEARYKAB0WIQQQ1ub6gR5ogjaKRmOGXBN6rc5S1gUCamNPvAAKCRCGXBN6rc5S 1jS3AP96xAV6tdo5fPUAIVGuhE+lXKoppDkmuQX1EC4XtI9KRgD/XzVEu0/IvVjA KfYQg+G7K9N5IJAuVGvicUoHa7EZrw4= =NZpC -----END PGP SIGNATURE----- --------------tmAUU7aaQUfp05UMAY0PS3Nq--