From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from canpmsgout02.his.huawei.com (canpmsgout02.his.huawei.com [113.46.200.217]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5C5344F85AD; Mon, 19 Oct 2026 12:48:56 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=113.46.200.217 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792414145; cv=none; b=o7nUoj+qc1Ctvc204lhqVAcMVR8iRKC2BAyCWuVQ/LEVD5zj4K/stKCNxZS7tsgXAwgAqfgnRN9B0Puil/hbC22IYkTSFkyScGPS8FwPUnPf+ZykmF+SocQaFzCvbKbv7mWQ9bL8S9S/ClSVwNTfrkeHHCQCOJxHOu001VDOUuE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1792414145; c=relaxed/simple; bh=nSpM0j3+znkzFmIU9xoQSupcFMEyLp7bXuizXMaf/k0=; h=Subject:To:CC:References:From:Message-ID:Date:MIME-Version: In-Reply-To:Content-Type; b=sv3nSJ6Ujn2CnPeHgqjL+/Zg1oSDlGTfsHA+FkgQSbJUCeAsCqdCfzmXDw75bBhGvkgkM4iOEZh9AGc/3HDZHgGJ18/GcEWUuOaIWf7ys/VqFGa8/QEdsGzchY3X+RwNKxcLMMk1UZBTlJyWAVQLrvR6iju2bbs3eLYBdFwNnn8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com; spf=pass smtp.mailfrom=huawei.com; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b=5nPKjafy; arc=none smtp.client-ip=113.46.200.217 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=huawei.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=huawei.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=huawei.com header.i=@huawei.com header.b="5nPKjafy" dkim-signature: v=1; a=rsa-sha256; d=huawei.com; s=dkim; c=relaxed/relaxed; q=dns/txt; h=From; bh=sQXqHgnR+1pIPsUZEl3zynhZARYK4/So3jnkyAxXf8g=; b=5nPKjafyrabzeYMbeC7CX7CvCEf/VurO0VfLru+paC6OxT8dAUxqnA/3sDANVSIoP4gpTLBEY ldxw8tzmZwGk51W8BfpHKFDJJD4RLHv1UV4A24RPMjZlgVQ/YUDwP77ggmhZAPfiuKNURMSWASF Xqc7BvH4tV0tVjx+5FQF5ZQ= Received: from mail.maildlp.com (unknown [172.19.162.140]) by canpmsgout02.his.huawei.com (SkyGuard) with ESMTPS id 4j7b2Q3NYlzcb48; Mon, 19 Oct 2026 20:48:46 +0800 (CST) Received: from whupemo200011.china.huawei.com (unknown [7.152.185.179]) by mail.maildlp.com (Postfix) with ESMTPS id F367C203AB; Mon, 19 Oct 2026 20:48:52 +0800 (CST) Received: from [10.174.178.46] (10.174.178.46) by whupemo200011.china.huawei.com (7.152.185.179) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.2.2562.45; Mon, 19 Oct 2026 20:48:51 +0800 Subject: Re: [PATCH] fs: rotate inodes whose page cache could not be dropped To: Nikolaos Karaolidis , Christian Brauner , Alexander Viro CC: Jan Kara , Mateusz Guzik , , , , References: <20261016102515.111285-1-nick@karaolidis.com> From: Zhihao Cheng Message-ID: <9ea0c46f-a2b2-b18b-6b69-ca035b005bbe@huawei.com> Date: Mon, 19 Oct 2026 20:48:50 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: <20261016102515.111285-1-nick@karaolidis.com> Content-Type: text/plain; charset="gbk"; format=flowed Content-Transfer-Encoding: 8bit X-ClientProxiedBy: kwepems200001.china.huawei.com (7.221.188.67) To whupemo200011.china.huawei.com (7.152.185.179) ÔÚ 2026/10/16 18:25, Nikolaos Karaolidis дµÀ: > When inode_lru_isolate() drops the page cache of an unused inode, it > has to unlock the list, so it returns LRU_RETRY and the walk restarts > at the head of the list, where the inode still is. If > invalidate_mapping_pages() could not empty the mapping, the restarted > walk strips the same inode again, and so on until nr_to_walk runs out. > Every walk of that list then ends on this inode, and nothing behind it > is reclaimed for as long as its cache stays. > > Before commit 2a0629834cd8 ("vfs: Don't evict inode under the inode lru > traversing context") the walker pinned the inode with a reference, and > dropping it in iput_final() set I_REFERENCED, so the restarted walk > rotated the inode to the tail. Set I_REFERENCED again when the mapping > is still populated after the invalidation, in the same i_lock section > that clears I_LRU_ISOLATING. inode_unpin_lru_isolating() now expects > i_lock to be held, like inode_pin_lru_isolating(). > > On CONFIG_HIGHMEM kernels this can happen to any unused inode: a folio > is left behind if it is locked, under writeback, spliced into a pipe, > or still in another CPU's LRU-add batch after being read. Without > HIGHMEM it happens to DAX inodes whose only entry is at index 0, which > mapping_shrinkable() lets onto the LRU and invalidate_mapping_pages() > never removes. > > Fixes: 2a0629834cd8 ("vfs: Don't evict inode under the inode lru traversing context") > Cc: stable@vger.kernel.org > Assisted-by: LLM > Signed-off-by: Nikolaos Karaolidis > --- > > Found while working on reclaim of inodes pinned by page cache in > ZONE_MOVABLE. > > Tested in QEMU/KVM on master af32da41b032 (v7.3-rc6-232), with lockdep > and KASAN enabled. A small init program makes one unused inode whose > page can't be invalidated, lets it reach the head of the inode LRU, > opens 2000 other files, does one "echo 2 > /proc/sys/vm/drop_caches" > and counts the inodes left via umount; kprobes count the > invalidate_mapping_pages() calls: > > without patch with patch > i386 HIGHMEM, file read 2000 of 2000 left, none left, > on another CPU 10300 strips, 1 inode 4 strips > i386 HIGHMEM, page same same > spliced into a pipe > x86_64, ext4 -o dax, same same > file mmap()ed > controls (no leftover, none left none left > shadow entry at index 0) > > 2a0629834cd8^ behaves like the patched kernel, 2a0629834cd8 like > master. On 5.15.y x86_64, where every unused inode with page cache is > on the LRU, the read-on-another-CPU case blocks the walk as well. > > With "echo 64M > /sys/fs/cgroup/memory.reclaim" instead of > drop_caches, the i386 pipe case does 262450 strips and frees nothing > without the patch, 40 strips and frees everything with it. In the DAX > case that write takes ~400ms with the patch instead of ~4ms: > invalidate_mapping_pages() counts the DAX entry it leaves behind as > reclaimed, so unpatched, the 64M are "reclaimed" by re-stripping one > inode in a tight loop while nothing is freed. > > The reproducer is a single C file; I can post it. > > An LLM was used to check the analysis against the code, write the > reproducer and draft the changelog; I have reviewed all of it. > > fs/inode.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > Reviewed-by: Zhihao Cheng > diff --git a/fs/inode.c b/fs/inode.c > index a9d37be390a1..1614a97ce953 100644 > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -593,12 +593,11 @@ static void inode_pin_lru_isolating(struct inode *inode) > > static void inode_unpin_lru_isolating(struct inode *inode) > { > - spin_lock(&inode->i_lock); > + lockdep_assert_held(&inode->i_lock); > WARN_ON(!(inode_state_read(inode) & I_LRU_ISOLATING)); > inode_state_clear(inode, I_LRU_ISOLATING); > /* Called with inode->i_lock which ensures memory ordering. */ > inode_wake_up_bit(inode, __I_LRU_ISOLATING); > - spin_unlock(&inode->i_lock); > } > > static void inode_wait_for_lru_isolating(struct inode *inode) > @@ -981,7 +980,13 @@ static enum lru_status inode_lru_isolate(struct list_head *item, > else > __count_vm_events(PGINODESTEAL, reap); > mm_account_reclaimed_pages(reap); > + > + spin_lock(&inode->i_lock); > + /* The walk restarts here: don't retry leftovers right away */ > + if (!mapping_empty(&inode->i_data)) > + inode_state_set(inode, I_REFERENCED); > inode_unpin_lru_isolating(inode); > + spin_unlock(&inode->i_lock); > return LRU_RETRY; > } > > > base-commit: af32da41b0327b9c6a37856ba82b6760d6c8d10e >