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 9FAFEC5AD7B for ; Mon, 10 Aug 2026 18:32:27 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 8B12C6B007B; Mon, 10 Aug 2026 14:32:26 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 861B76B008A; Mon, 10 Aug 2026 14:32:26 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 72A046B0093; Mon, 10 Aug 2026 14:32:26 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0017.hostedemail.com [216.40.44.17]) by kanga.kvack.org (Postfix) with ESMTP id 3FF446B007B for ; Mon, 10 Aug 2026 14:32:26 -0400 (EDT) Received: from smtpin14.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay07.hostedemail.com (Postfix) with ESMTP id 599DC16025E for ; Mon, 10 Aug 2026 18:32:24 +0000 (UTC) X-FDA: 85086205008.14.AD65E01 Received: from mail-pl1-f182.google.com (mail-pl1-f182.google.com [209.85.214.182]) by imf08.hostedemail.com (Postfix) with ESMTP id 851F816000A for ; Mon, 10 Aug 2026 18:32:22 +0000 (UTC) Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=google.com header.s=20251104 header.b=PZtUpNit; spf=pass (imf08.hostedemail.com: domain of cmllamas@google.com designates 209.85.214.182 as permitted sender) smtp.mailfrom=cmllamas@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786386742; b=yXbLeGfhPvs2zd515goftLIvIpuXKvgPKbYDKe1xzD5qpeMOERVOSCLOvcub+esixVnzkT O2paJ7pNBVwN9ZUeXTZX/M4wIU9PVu+k2V4bMfFpzrx0OWg6obNZ2PvtzNN5Px4pObqY3A 6VohjeiRizEmPGhq9uYw+HLBTcmaQCk= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=google.com header.s=20251104 header.b=PZtUpNit; spf=pass (imf08.hostedemail.com: domain of cmllamas@google.com designates 209.85.214.182 as permitted sender) smtp.mailfrom=cmllamas@google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786386742; 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:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=Yc1i9jCZ38+WjTOLsbw1yfhU6KnLG4orWewt9NM2biU=; b=nhnDMMbM0yclRbQISUzuJsYVJVVRBMfgFEriBfX3xMdxPV4qej2Y+iPIM2Yys1mDvn8Jy5 yNpxkS/wI4q8GQ3MoA5Du896JuyV5JrTtc4UIekhinj2BrW8ipIsXFo8e5siABi2f6IkTs J2XUm9ADLohzROMYZGhrxB++rCpWQLE= Received: by mail-pl1-f182.google.com with SMTP id d9443c01a7336-2ccdf36f63dso17055ad.0 for ; Mon, 10 Aug 2026 11:32:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786386741; x=1786991541; darn=kvack.org; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:from:to:cc:subject:date:message-id:reply-to:content-type; bh=Yc1i9jCZ38+WjTOLsbw1yfhU6KnLG4orWewt9NM2biU=; b=PZtUpNitMrabOWDq3CEdpMPF0y2IuCFGXKLagKtBZXtWTK+Yrb4hyVEL5SDkB09Onc 5BOf6pm9h39GpZmXxk3AH274FubKDinLAHsfUd2+c6+//j8CxRPHadKC8uZ0xwOHnis+ KNjyz7R8EhjS6JBsbqJkaqP+YB9sY6f35z1DlyE/W+lqkhs3pSp0Hvh1IHA28GdO30jO /apP8xnj06bYhjUbAfwoTuDblk4vGbNkvmSHrpA2HBb0bILfzgUO/JkPn2ENWA7Bd57R gVAevIQGbktx6Ui16HTSkN6gOfRW0ZTKvCpQLBNYkkPrjI7w16DNRx9cRgk88B1Eo3mK LLeg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786386741; x=1786991541; h=in-reply-to:content-transfer-encoding:content-disposition :content-type:mime-version:references:message-id:subject:cc:to:from :date:x-gm-gg:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to:content-type; bh=Yc1i9jCZ38+WjTOLsbw1yfhU6KnLG4orWewt9NM2biU=; b=HXTYkwpjSvzIk3RXp8t6FhHFmHEPVhPJvsACkSVlJNDp9vcCOXpsn7aj0FAg8M3sI5 9v48CxcR3Dj8aARj56Qm4tWzv5HPB6UXSJF4tFPM6opm/TU1iwwEN/oRxkLVnUM2QLGP 8Nq4J14CdbF3bB4+QiNcD0Y4CwWwlgZuBEWl+vxcYE3Nc5j1UHsH6jS9IMTYdoYB0Ccj KVvKAPVC3cG+H/frkU6xP94pNL3FW8ZN63sN9GjpdLP03PU0xJRFp85+4Ju2jJ/yLWrs ZyoawqZJlUDesXM+Hj362T3CCAwkRaa81XRK4PGC6MxGclG8KN14MKEolywQVaePefNZ xliA== X-Forwarded-Encrypted: i=1; AHgh+RqLPeou9hgxdeSeGx/WTyt84bjaschqdGygTNv5h6ltH6VKacteNJ/UmKGrp4YG1pvo5c9Qa28vsg==@kvack.org X-Gm-Message-State: AOJu0Yzh6x8MhrtqcO3QP3IsX9pGzxtmGwCJRlVav1zTH9Ma7AHVXId7 MYE33nwkUl2mAOjYNx5G8N7Smg6jYsLuqnEHOKsR0WnqYJ66M4Js76yaU/06o+F/aQ== X-Gm-Gg: AR+sD13daNCQ11wcnziUIuB+Q1qqZ8YxWaHJ2LtUxjCbdmu/zPl1kkRzkjV6x07CdRQ Qmr/Zh3MxCyncvbhh2q9ApPqH20AOjnOIbYwk5Fvt1kgu52gCIgGCKY9kZTI1FaTrSXg533+OB9 gv+UQPTiQEQdCYmnozfagzm54zrjroci2SZX/ShemRiFsrx2UMKs8zr/ODd26tRw7RUd2sNPpFp 16voMwjR/b5EPMQqK5h5uTtQgX3iLx3GtSEeD62TXyugKuc0+WyJYJMpENDPtahLHSd1MgiO27g JnQvelGx+R5ADucPbqmL4d+3hyM2kMd8ae5ofG9Emk6wcRsheMW1TWNFdImIJqx31ebllMhJyc4 HLprWHccEcgtoQjrM9oOCPS06UWh3d5ddmwSPn87wU29kb8KKBnIXTiDPtHLq6aNynNnQiuhOgt O690q/X9B//k2YbOoMYN0vRBmNygrB1lL9wO/c2TgeRnVFgTN1c94EvJAAn7UZhjCXg5mKFLk8F 8pJbMIES4XX6Mv+cdVf25pL6mERkqLtIucsAgeZVDXpJiMNDb6TQHiKpgJL5B6q35VVUy6dHf4N H/e8G18= X-Received: by 2002:a17:903:2ce:b0:2ca:6bf:5bac with SMTP id d9443c01a7336-2d3105ceb62mr1449205ad.8.1786386740920; Mon, 10 Aug 2026 11:32:20 -0700 (PDT) Received: from google.com (193.67.125.34.bc.googleusercontent.com. [34.125.67.193]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-cbe8f35b16bsm4507503a12.20.2026.08.10.11.32.19 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 10 Aug 2026 11:32:19 -0700 (PDT) Date: Mon, 10 Aug 2026 18:32:15 +0000 From: Carlos Llamas To: Suren Baghdasaryan Cc: akpm@linux-foundation.org, dave.hansen@linux.intel.com, Liam.Howlett@oracle.com, ljs@kernel.org, david@kernel.org, willy@infradead.org, shakeel.butt@linux.dev, vbabka@kernel.org, jannh@google.com, aliceryhl@google.com, arve@android.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 v4 2/5] binder: Make shrinker rely solely on per-VMA lock Message-ID: References: <20260806200548.3124802-1-surenb@google.com> <20260806200548.3124802-3-surenb@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260806200548.3124802-3-surenb@google.com> X-Rspamd-Queue-Id: 851F816000A X-Stat-Signature: sx5ssxx67z4busymt4bis4zixdc6arib X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1786386742-504291 X-HE-Meta: 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 lbTKKZOh 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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 Thu, Aug 06, 2026 at 01:05:45PM -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. > The removal of the fallback does not affect NOMMU case because binder > driver depends on CONFIG_MMU. > > 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 > Cc: Andrew Morton > Cc: "Liam R. Howlett" > Cc: Vlastimil Babka > Cc: Shakeel Butt > Cc: linux-mm@kvack.org > Cc: Greg Kroah-Hartman > Cc: Arve Hjønnevåg > Cc: Todd Kjos > Cc: Christian Brauner > Cc: Carlos Llamas > Cc: Alice Ryhl > Cc: "David S. Miller" > Cc: David Ahern > Cc: netdev@vger.kernel.org > --- > drivers/android/binder_alloc.c | 45 ++++++++++++++++------------------ > 1 file changed, 21 insertions(+), 24 deletions(-) > > diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c > index e4488ad86a65..c13a588c37de 100644 > --- a/drivers/android/binder_alloc.c > +++ b/drivers/android/binder_alloc.c > @@ -1142,7 +1142,6 @@ enum lru_status binder_alloc_free_page(struct list_head *item, > struct vm_area_struct *vma; > struct page *page_to_free; > unsigned long page_addr; > - int mm_locked = 0; > size_t index; > > if (!mmget_not_zero(mm)) > @@ -1151,27 +1150,25 @@ enum lru_status binder_alloc_free_page(struct list_head *item, > index = mdata->page_index; > page_addr = alloc->vm_start + index * PAGE_SIZE; > > - /* attempt per-vma lock first */ > + /* > + * Attempt per-vma lock. This is essentially a > + * "trylock". It can fail even if the VMA exists > + * for 'page_addr'. > + */ Do we need to explain how lock_vma_under_rcu() works here? > vma = lock_vma_under_rcu(mm, page_addr); > if (!vma) { > - /* fall back to mmap_lock */ > - if (!mmap_read_trylock(mm)) > - goto err_mmap_read_lock_failed; > - mm_locked = 1; > - vma = vma_lookup(mm, page_addr); > + /* > + * If the vma exists, we can't continue because we cannot > + * remove the page from the vma. However, if the vma was > + * unmapped, it's okay to continue. > + */ > + if (binder_alloc_is_mapped(alloc)) > + goto err_vma_lock_failed; The comments seem redundant, the label is enough. This works: vma = lock_vma_under_rcu(mm, page_addr); if (!vma && binder_alloc_is_mapped(alloc)) goto err_vma_lock_failed; > } > > if (!mutex_trylock(&alloc->mutex)) > goto err_get_alloc_mutex_failed; > > - /* > - * Since a binder_alloc can only be mapped once, we ensure > - * the vma corresponds to this mapping by checking whether > - * the binder_alloc is still mapped. > - */ > - if (vma && !binder_alloc_is_mapped(alloc)) > - goto err_invalid_vma; > - This introduces an "extra" change. We'll now release pages without a valid vma (e.g. after munmap()). Before, these pages were expected to be released via close() in binder_alloc_deferred_release() later. I don't see anything wrong with it. However, it does seem out of the scope of this patch which just drops the mmap_read_lock() calls. Or at least I don't see how this part is necessary. > trace_binder_unmap_kernel_start(alloc, index); > > page_to_free = alloc->pages[index]; > @@ -1182,7 +1179,12 @@ enum lru_status binder_alloc_free_page(struct list_head *item, > list_lru_isolate(lru, item); > spin_unlock(&lru->lock); > > - if (vma) { > + /* > + * Since a binder_alloc can only be mapped once, we ensure > + * the vma corresponds to this mapping by checking whether > + * the binder_alloc is still mapped. > + */ > + if (vma && binder_alloc_is_mapped(alloc)) { > trace_binder_unmap_user_start(alloc, index); > > zap_vma_range(vma, page_addr, PAGE_SIZE); > @@ -1191,23 +1193,18 @@ enum lru_status binder_alloc_free_page(struct list_head *item, > } > > mutex_unlock(&alloc->mutex); > - if (mm_locked) > - mmap_read_unlock(mm); > - else > + if (vma) > vma_end_read(vma); > mmput_async(mm); > binder_free_page(page_to_free); > > return LRU_REMOVED_RETRY; > > -err_invalid_vma: > mutex_unlock(&alloc->mutex); This mutex_unlock() is now dead-code. > err_get_alloc_mutex_failed: > - if (mm_locked) > - mmap_read_unlock(mm); > - else > + if (vma) > vma_end_read(vma); > -err_mmap_read_lock_failed: > +err_vma_lock_failed: > mmput_async(mm); > err_mmget: > return LRU_SKIP; > -- > 2.55.0.654.g21b8a5bc05-goog >