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Mon, 7 Oct 2024 11:47:28 +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 IgElHFDKA2d4QwAAD6G6ig (envelope-from ); Mon, 07 Oct 2024 11:47:28 +0000 Message-ID: Date: Mon, 7 Oct 2024 13:50:06 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: Remove misleading 'unlikely' hint in vms_gather_munmap_vmas() To: Breno Leitao , Andrew Morton , "Liam R. Howlett" , Lorenzo Stoakes Cc: kernel-team@meta.com, "open list:VMA" , open list References: <20241004164832.218681-1-leitao@debian.org> From: Vlastimil Babka Content-Language: en-US In-Reply-To: <20241004164832.218681-1-leitao@debian.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Action: no action X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 8EFAF8000D X-Stat-Signature: c5byixuziui85foh7gr8myg68447p1fs X-Rspam-User: X-HE-Tag: 1728301650-532754 X-HE-Meta: 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 bc8OmZgi 8cRYFaMqzms7Jagb/jB1KAQl29ycWSl4N8vds5rC1xZu2e10JxPCtLgzl1wtv6hQEQ0lsRy+Hbh92PY8sP47/y8sMYuaCSbM7H5xnDJQ6oJnFGPP6dh7fzuPMw2jh23JLhW1zAvDkkompeFb6f2IkM8eWts8qKLNXnzCEnFMuPXRP8nbVerbcigoJCG1hLlOX2YuBANL1qUyLtKpF7mYRDYMOQfZmtRwrtQOMWcX9h3e6rH4fOtqA7r/QboSIpM4TOJOgGa54nxlEVXv2enPp9scvCrKRruZIy6neuLAYZ6xe4IuR5rjf/Vs2IyCbtQKviq8x8bVJtWxdX0xtjQz73BiMWzDet+JRCsl2 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 10/4/24 6:48 PM, Breno Leitao wrote: > Performance analysis using branch annotation on a fleet of 200 hosts > running web servers revealed that the 'likely' hint in > vms_gather_munmap_vmas() was 100% consistently incorrect. In all > observed cases, the branch behavior contradicted the hint. > > Remove the 'unlikely' qualifier from the condition checking 'vms->uf'. > By doing so, we allow the compiler to make optimization decisions based > on its own heuristics and profiling data, rather than relying on a > static hint that has proven to be inaccurate in real-world scenarios. > > Signed-off-by: Breno Leitao Acked-by: Vlastimil Babka > --- > mm/vma.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/mm/vma.c b/mm/vma.c > index 4737afcb064c..9d4fe794dd07 100644 > --- a/mm/vma.c > +++ b/mm/vma.c > @@ -1250,7 +1250,7 @@ int vms_gather_munmap_vmas(struct vma_munmap_struct *vms, > else if (is_data_mapping(next->vm_flags)) > vms->data_vm += nrpages; > > - if (unlikely(vms->uf)) { > + if (vms->uf) { > /* > * If userfaultfd_unmap_prep returns an error the vmas > * will remain split, but userland will get a