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From: Hao Li To: Vlastimil Babka Cc: Harry Yoo , Petr Tesarik , Christoph Lameter , David Rientjes , Roman Gushchin , Andrew Morton , Uladzislau Rezki , "Liam R. Howlett" , Suren Baghdasaryan , Sebastian Andrzej Siewior , Alexei Starovoitov , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, bpf@vger.kernel.org, kasan-dev@googlegroups.com Subject: Re: [PATCH v3 14/21] slab: simplify kmalloc_nolock() Message-ID: <2tvnelafuozzzfyvmxvflqmx2sepgy7ottnw4n2trkh33rrk6b@oewlapq3smvg> References: <20260116-sheaves-for-all-v3-0-5595cb000772@suse.cz> <20260116-sheaves-for-all-v3-14-5595cb000772@suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260116-sheaves-for-all-v3-14-5595cb000772@suse.cz> X-Migadu-Flow: FLOW_OUT X-Stat-Signature: q47d3nbcbq3ptrh3tybzdb4pewh3c9hy X-Rspamd-Queue-Id: 2A6011C000A X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1768910812-33269 X-HE-Meta: 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 7E/FvIl3 rAu6lFwp8JyAhfrPfKUiXrZnV0BAKpBamMsmypiC2J9NoYO/BXGAiShAHlWG0J+tPb0g6KmoP4/3DgSUBCQln3KiU46CLVz+nXgzTwCzWiYK2r3FVEQGvCX0AhlhHtrvnndXebfhPu6GTXtdlDTdmUbl4JAKS343aC+/on/IUdKJeBr8bJbqmMvEMnwpUPoxDFmVLVcXUymxbUtM7rP7xUt9nYJon0obSrlMQy8RVO3xs4GwUvrQ1JfarJCdWn0HeWo78 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 Fri, Jan 16, 2026 at 03:40:34PM +0100, Vlastimil Babka wrote: > The kmalloc_nolock() implementation has several complications and > restrictions due to SLUB's cpu slab locking, lockless fastpath and > PREEMPT_RT differences. With cpu slab usage removed, we can simplify > things: > > - relax the PREEMPT_RT context checks as they were before commit > a4ae75d1b6a2 ("slab: fix kmalloc_nolock() context check for > PREEMPT_RT") and also reference the explanation comment in the page > allocator > > - the local_lock_cpu_slab() macros became unused, remove them > > - we no longer need to set up lockdep classes on PREEMPT_RT > > - we no longer need to annotate ___slab_alloc as NOKPROBE_SYMBOL > since there's no lockless cpu freelist manipulation anymore > > - __slab_alloc_node() can be called from kmalloc_nolock_noprof() > unconditionally. It can also no longer return EBUSY. But trylock > failures can still happen so retry with the larger bucket if the > allocation fails for any reason. > > Note that we still need __CMPXCHG_DOUBLE, because while it was removed > we don't use cmpxchg16b on cpu freelist anymore, we still use it on > slab freelist, and the alternative is slab_lock() which can be > interrupted by a nmi. Clarify the comment to mention it specifically. > > Signed-off-by: Vlastimil Babka > --- > mm/slab.h | 1 - > mm/slub.c | 144 +++++++++++++------------------------------------------------- > 2 files changed, 29 insertions(+), 116 deletions(-) > Looks good to me. Reviewed-by: Hao Li -- Thanks, Hao