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AFNElJ/CtWzcqLikQyis12s2UbYuimx8WKHuS5Rx4Fqz6ml/uBcuAkBOIEfE9gbdvz4waBLWuKkv1o88mA==@kvack.org X-Gm-Message-State: AOJu0YwaSaU86owahsAtP5PXCvxb74NSpT11Ujt38zb1dbmTZMOZBi7E bCOC32bdMUGqBxqHYqd6dJAvCgOoB4cBpVLRiffsrztQuXvlPhdH2mvp7X1S9G6+B4KjkV4kzm8 CYRti8ZHszC8wTZmxpg== X-Received: from wmbdn18.prod.google.com ([2002:a05:600c:6552:b0:489:1f67:5a81]) (user=aliceryhl job=prod-delivery.src-stubby-dispatcher) by 2002:a05:600c:698d:b0:489:1ba8:5be9 with SMTP id 5b1f17b1804b1-48e706f0e53mr217152875e9.29.1778576163910; Tue, 12 May 2026 01:56:03 -0700 (PDT) Date: Tue, 12 May 2026 08:56:02 +0000 In-Reply-To: Mime-Version: 1.0 References: <20260507-binder-shrinker-lockvma-v1-1-76e3406bbfa6@google.com> Message-ID: Subject: Re: [PATCH] rust_binder: use lock_vma_under_rcu() in shrinker From: Alice Ryhl To: Lorenzo Stoakes Cc: Greg Kroah-Hartman , Carlos Llamas , "Liam R. Howlett" , Miguel Ojeda , Boqun Feng , Gary Guo , "=?utf-8?B?QmrDtnJu?= Roy Baron" , Benno Lossin , Andreas Hindborg , Trevor Gross , Danilo Krummrich , linux-mm@kvack.org, rust-for-linux@vger.kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" X-Stat-Signature: e687m4m8fyn7fi9bfp3yihxisja7kcmb X-Rspamd-Queue-Id: 7F278100008 X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1778576165-297008 X-HE-Meta: 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 jEQDnkv9 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, May 11, 2026 at 02:19:42PM +0100, Lorenzo Stoakes wrote: > On Thu, May 07, 2026 at 11:07:47AM +0000, Alice Ryhl wrote: > > The shrinker callback currently uses the mmap read trylock operation to > > attempt to access the vma, but it's generally better to only lock the > > vma instead of the whole mmap when you can. > > > > When lock_vma_under_rcu() fails, there is no reason to lock the mmap > > lock instead because it's already a trylock operation that is allowed to > > fail. > > > > Signed-off-by: Alice Ryhl > > This seems similar to Dave's patch [0], not sure if it was inspired by that? :) > > [0]:https://lore.kernel.org/all/20260429181957.7511C256@davehans-spike.ostc.intel.com/ I was reminded by that change, but it's been on my list since commit a0b9b0f1433c ("rust_binder: use lock_vma_under_rcu() in use_page_slow()"). > In any case the general approach seems sane to me, as rust code I can't really > review it properly, but aside from the comment below (presumably that's fine) it > conceptually LGTM so: > > Acked-by: Lorenzo Stoakes > > > --- > > drivers/android/binder/page_range.rs | 24 +++++++++++------------- > > 1 file changed, 11 insertions(+), 13 deletions(-) > > > > diff --git a/drivers/android/binder/page_range.rs b/drivers/android/binder/page_range.rs > > index e54a90e62402..e82a5523804f 100644 > > --- a/drivers/android/binder/page_range.rs > > +++ b/drivers/android/binder/page_range.rs > > @@ -705,7 +705,7 @@ fn drop(self: Pin<&mut Self>) { > > let page; > > let page_index; > > let mm; > > - let mmap_read; > > + let vma_read; > > let mm_mutex; > > let vma_addr; > > let range_ptr; > > @@ -728,17 +728,18 @@ fn drop(self: Pin<&mut Self>) { > > None => return LRU_SKIP, > > }; > > > > - mmap_read = match mm.mmap_read_trylock() { > > - Some(guard) => guard, > > - None => return LRU_SKIP, > > - }; > > - > > // We can't lock it normally here, since we hold the lru lock. > > let inner = match range.lock.try_lock() { > > Some(inner) => inner, > > None => return LRU_SKIP, > > }; > > > > + vma_addr = inner.vma_addr; > > + vma_read = match mm.lock_vma_under_rcu(vma_addr) { > > + Some(guard) => guard, > > + None => return LRU_SKIP, > > + }; > > + > > One question here - are we good to do this _after_ locking the 'inner' lock > above? Well, it's a spinlock so unless lock_vma_under_rcu() can sleep it should be fine. Though we also hold *another* spinlock here, so if it can sleep, we couldn't take it before `inner` either. Alice