From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id E66FEC55179 for ; Mon, 3 Aug 2026 13:39:07 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id D3DCD6B00DE; Mon, 3 Aug 2026 09:39:06 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CEE246B00DF; Mon, 3 Aug 2026 09:39:06 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id BDD876B00E0; Mon, 3 Aug 2026 09:39:06 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 8FC3F6B00DE for ; Mon, 3 Aug 2026 09:39:06 -0400 (EDT) Received: from smtpin13.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay06.hostedemail.com (Postfix) with ESMTP id 0BB66A1654 for ; Mon, 3 Aug 2026 11:11:58 +0000 (UTC) X-FDA: 85059693516.13.D5345F8 Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by imf27.hostedemail.com (Postfix) with ESMTP id 5E82040006 for ; Mon, 3 Aug 2026 11:11:56 +0000 (UTC) Authentication-Results: imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=VYy7zN9D; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1785755516; b=XqsCKZtxlNLPRACUozriUoELICBsQBAgh8VbQMjiyaa2PokO8FEx5gsM5Qmzo6ICRWj6RG qyX2e25DZ4M7X+sCFpc/nioRvxTaGKYzAcArKPgjZ9cjhgVu21Vz/8T3cCiYvj1dZkpbRU Y9gy8Q49eJdYs9Jy1pVr5q3qWztnY7U= ARC-Authentication-Results: i=1; imf27.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20260515 header.b=VYy7zN9D; spf=pass (imf27.hostedemail.com: domain of ljs@kernel.org designates 172.234.252.31 as permitted sender) smtp.mailfrom=ljs@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1785755516; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=WJjA9p12tFsV6zkH5AhowSQn8yCnJRFh98dmbQ7S74A=; b=OLhBt6hK8ESDPG/ZYxZIVD390QgfmW8nJXU94icO+mU6TWaTBSneqYrF00+B2SOgC829hu IHBbYn76gGQde4vp1tgXyTYIEGhoYlzXqTA5JTEMCDV6QMmz9xGQYdUk3Wt24fqcIFY3iM LhM0dUsft9nrmKyvuGc0JzptQv1VFKc= Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 832B6408AA; Mon, 3 Aug 2026 11:11:55 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id F10E51F000E9; Mon, 3 Aug 2026 11:11:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1785755515; bh=WJjA9p12tFsV6zkH5AhowSQn8yCnJRFh98dmbQ7S74A=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=VYy7zN9DQKeubwiuG+IrgbF+ryVDfowZogKwDDz4NWIOW5URub+pUL/pVNmMh24YZ tpQUlAF7BYw18DWmWlNETeMUjNpu9opaVkR9p1HpuWg0MN4zG9782rUewY1BG+7cyO Xo0jlKsFEPT4Ar0HfyxhRJtEy1IurhpiRKDK+IOiu2qFXH9JxL9D2eMsfRjz9lK/+f RPVTiqwaX4ty51kutN6Q8ZKy9cpufqJH56nA5zFp0w3wfg0QYMnNu4WDpiSA5qcAvs H+jL4E4WW4PpVHOgclHuw5ywFycKD25HzsTuONfE0U55xDuEy+13soDMv86Kv8S27G ZImetKrLspSxQ== Date: Mon, 3 Aug 2026 12:11:37 +0100 From: "Lorenzo Stoakes (ARM)" To: Alice Ryhl Cc: Suren Baghdasaryan , akpm@linux-foundation.org, dave.hansen@linux.intel.com, Liam.Howlett@oracle.com, david@redhat.com, willy@infradead.org, shakeel.butt@linux.dev, vbabka@kernel.org, jannh@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 Subject: Re: [PATCH v3 2/5] binder: Make shrinker rely solely on per-VMA lock Message-ID: References: <20260802215459.2769283-1-surenb@google.com> <20260802215459.2769283-3-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 5E82040006 X-Stat-Signature: x5m4muhfascapujgorrrg78sy8h4utf9 X-Rspam-User: X-HE-Tag: 1785755516-304075 X-HE-Meta: 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 px0oBCbR 7nQY2ur2LWu/Bdi+VB169bskB8ONMlbM4J6XLAS/+BCSO3JCrM2hM3lRjUcp1vWbwzB880LsRnK6VjmgPysZ8huU9mvuXZI+AlKzK+vf6gPNp+Bf6Gfz8U3HAkwEIl9frCKrmJ8CF345cEzo/rsAhrCqtOqm0/urQlq4sLjuSxg5oDUUyF1WoKlOXFAbEC+fBJzxfSZ+QZOeDs7HY8sVErU+dzpF7zSaFxFUjsUiBizsTjEbXFNa2fjMgjfTNuPuT5c8qt4tQebMrvMXlhjxM6NdR8RNui02635eI8k4Ptii6fdvBo3bRvKhxs4LiSam5OcyTuRsSTQFGGQK3XyUKaOTUfTZ309mGPcmmZKrt8BwxO6emxvwd2vxmKg== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Aug 03, 2026 at 11:50:41AM +0100, Lorenzo Stoakes (ARM) wrote: > On Mon, Aug 03, 2026 at 09:48:19AM +0000, Alice Ryhl wrote: > > On Sun, Aug 02, 2026 at 02:54:56PM -0700, Suren Baghdasaryan wrote: > > > From: Dave Hansen > > > > > > tl;dr: lock_vma_under_rcu() is already a trylock. No need to do both > > > it and mmap_read_trylock(). > > > > > > Long Version: > > > > > > == Background == > > > > > > Historically, binder used an mmap_read_trylock() in its shrinker code. > > > This ensures that reclaim is not blocked on an mmap_lock. Commit > > > 95bc2d4a9020 ("binder: use per-vma lock in page reclaiming") added > > > support for the per-VMA lock, but left mmap_read_trylock() as a > > > fallback. > > > > > > This was presumably because the per-VMA locking can fail for several > > > reasons and most (all?) lock_vma_under_rcu() callers have a fallback > > > to mmap_read_trylock(). > > > > > > == Problem == > > > > > > The fallback is not worth the complexity here. lock_vma_under_rcu() is > > > essentially already a non-blocking trylock. The main reason it fails > > > is also the reason mmap_read_trylock() fails: something is holding > > > mmap_write_lock(). > > > > > > The only remedy for a collision with mmap_write_lock() is to wait, > > > which this code can not do. So the "fallback" after > > > lock_vma_under_rcu() failure is not really a fallback: it is really > > > likely to just be retrying in vain. That retry in an of itself isn't > > > horrible. But it adds complexity. > > > > > > == Solution == > > > > > > Now that per-VMA locks are universally available, lock_vma_under_rcu() > > > will not persistently fail. Rely on it alone and simplify the code. > > > > > > Full disclosure: I originally tried to do this with > > > lock_vma_under_rcu_wait(), but it did not fit well with the mmap_lock > > > trylock semantics. Claude caught this in a review and suggested the > > > approach in this path. It seemed sane to me. So, Suggesed-by: Claude, > > > I guess. > > > > > > Signed-off-by: Dave Hansen > > > Signed-off-by: Suren Baghdasaryan > > > > Reviewed-by: Alice Ryhl > > Is there anything on the rust side that needs to be changed also? Ah ok addressed in 4/5, disregard :) > > -- > Cheers, Lorenzo -- Cheers, Lorenzo