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t=1785765699; bh=WncJv2kkcU64xKPGNQ9beukr0q+5pv5G1Ub8Qx4hfik=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=npJot8k/nrdn2nthtMpZON/6+VLaq8SVi8n+4nzYI0Jk2DSK5qwvIOA2D3oOkYQh1 f3q1+vu33VbW5bjt0uiNre4iWtGzntus2qu1QxZJLVnfpM00USX/UMGDHcMBYLJLh+ SCyj29wXRdSdHv5CHVJ1eTDd8wADiAo1t+EUvGN97K98lm32Sopdid6Do79v2v61Qw 3Tw+Tf1ERJbiE/d2ZmuATr9wgacAy9Thola6shj+ZwFFKh044KBuin47utz8u6lh12 Gos65PSTbKmdBKNI+sc/kNiy4T9a71yIJeOheQjkcjeeEpu5z25UvfgP7UraGMPldT bg/fIPFuUsPDg== Message-ID: Date: Mon, 3 Aug 2026 16:01:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 1/5] mm: Make per-VMA locks available universally Content-Language: en-US To: Suren Baghdasaryan , akpm@linux-foundation.org Cc: dave.hansen@linux.intel.com, Liam.Howlett@oracle.com, ljs@kernel.org, david@redhat.com, willy@infradead.org, shakeel.butt@linux.dev, jannh@google.com, aliceryhl@google.com, arve@android.com, cmllamas@google.com, christian@brauner.io, tkjos@android.com, dsahern@kernel.org, davem@davemloft.net, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, netdev@vger.kernel.org References: <20260802215459.2769283-1-surenb@google.com> <20260802215459.2769283-2-surenb@google.com> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: C67FB180003 X-Stat-Signature: 1aza71enp3gzx8iaxn1dj9ogjqmaay33 X-Rspam-User: X-HE-Tag: 1785765700-144950 X-HE-Meta: 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 EfErQsYr t3txoNcPRT8Qz/6cMGd1cP6b/q7x2Rh3H2QAWkR3btY42yjwi4yImMYEykZC7DwswsEjNSW8C7FqSR6s5gB52RsdoGeoYKDVNm943JNEFve658sr8JWVW/0bzzjwxGG57A7TpfqZ4aVRCHEEwHPTt7w1qJDgKZd7nSHIGq1lEJNoXg49VJromoXYqdIq0FoHN0CkQe0UhKqekKW6Q+br1W+cetGI8RWAXXaAvF1uPJSptwPjvQF/Ab6ognhn143wqRFOYvtmPF5yIUnrukDOTXB4d3d/CO93+vuCfnNXV9m2MiSzvPMQ16S3ctx6sln6CPsuFyOmetQSWZ6TDs4OXzs9smekozkMDzJv9ROUuiJTE/WoLGeF4+ISG/FFN1vv0AnqEMmQKYEG/hTcNpaVMBly8MQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 8/2/26 23:54, Suren Baghdasaryan wrote: > From: Dave Hansen > > The per-VMA locks have been around for several years. They've had some > bugs worked out of them and have seen quite wide use. However, they > are still only available when architectures explicitly enable them. > Remove the conditional compilation around the per-VMA locks, making > them available on all architectures and configs. > > The approach up to now seemed to be to add ARCH_SUPPORTS_PER_VMA_LOCK > when the architecture started using per-VMA locks in the fault > handler. But, contrary to the naming, the Kconfig option does not > really indicate whether the architecture supports per-VMA locks or > not. It is more of a marker for whether the architecture is likely to > benefit from per-VMA locks. > > To me, the most important thing side-effect of universal availability > is letting per-VMA locks be used in SMP=n configs. This lets us use > per-VMA locking in all x86 code without fallbacks. > > Overall, this just generally makes the kernel simpler. Just look at > the diffstat. It also opens the door to users that want to use the > per-VMA locks in common code. Doing *that* brings additional > simplifications. > > The downside of this is adding some fields to vm_area_struct and > mm_struct. There are likely ways to optimize this, especially for > things like SMP=n configs. For now, do the simplest thing: use the > same implementation everywhere. > > Signed-off-by: Dave Hansen > Signed-off-by: Suren Baghdasaryan Reviewed-by: Vlastimil Babka (SUSE) Nits: > diff --git a/mm/Kconfig b/mm/Kconfig > index 060190e12bce..77103b46b679 100644 > --- a/mm/Kconfig > +++ b/mm/Kconfig > @@ -1425,19 +1425,6 @@ config LRU_GEN_STATS > config LRU_GEN_WALKS_MMU > def_bool y > depends on LRU_GEN && ARCH_HAS_HW_PTE_YOUNG > -# } I think either leave this in place, or remove the line above with "# multi-gen LRU {" as well? > - > -config ARCH_SUPPORTS_PER_VMA_LOCK > - def_bool n > - > -config PER_VMA_LOCK > - def_bool y > - depends on ARCH_SUPPORTS_PER_VMA_LOCK && MMU && SMP > - help > - Allow per-vma locking during page fault handling. > - > - This feature allows locking each virtual memory area separately when > - handling page faults instead of taking mmap_lock. > > config LOCK_MM_AND_FIND_VMA > bool ... > diff --git a/rust/kernel/mm.rs b/rust/kernel/mm.rs > index 4764d7b68f2a..2633e704c83d 100644 > --- a/rust/kernel/mm.rs > +++ b/rust/kernel/mm.rs > @@ -174,26 +174,20 @@ pub unsafe fn from_raw<'a>(ptr: *const bindings::mm_struct) -> &'a MmWithUser { > /// When per-vma locks are disabled, this always returns `None`. > #[inline] > pub fn lock_vma_under_rcu(&self, vma_addr: usize) -> Option> { > - #[cfg(CONFIG_PER_VMA_LOCK)] > { > // SAFETY: Calling `bindings::lock_vma_under_rcu` is always okay given an mm where > // `mm_users` is non-zero. > let vma = unsafe { bindings::lock_vma_under_rcu(self.as_raw(), vma_addr) }; > - if !vma.is_null() { > - return Some(VmaReadGuard { > - // SAFETY: If `lock_vma_under_rcu` returns a non-null ptr, then it points at a > - // valid vma. The vma is stable for as long as the vma read lock is held. > - vma: unsafe { VmaRef::from_raw(vma) }, > - _nts: NotThreadSafe, > - }); > + if vma.is_null() { > + return None; > } > + Some(VmaReadGuard { > + // SAFETY: If `lock_vma_under_rcu` returns a non-null ptr, then it points at a > + // valid vma. The vma is stable for as long as the vma read lock is held. > + vma: unsafe { VmaRef::from_raw(vma) }, > + _nts: NotThreadSafe, > + }) > } With the "#[cfg(CONFIG_PER_VMA_LOCK)]" does this still need to be in a { } block? > - > - // Silence warnings about unused variables. > - #[cfg(not(CONFIG_PER_VMA_LOCK))] > - let _ = vma_addr; > - > - None > } > > /// Lock the mmap read lock.