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Message-ID: <20200220175400.GB2902@twin.jikos.cz>
Date: Thu, 20 Feb 2020 18:54:00 +0100
From: David Sterba <dsterba@...e.cz>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, linux-btrfs@...r.kernel.org,
linux-erofs@...ts.ozlabs.org, linux-ext4@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net, cluster-devel@...hat.com,
ocfs2-devel@....oracle.com, linux-xfs@...r.kernel.org
Subject: Re: [PATCH v7 00/23] Change readahead API
On Wed, Feb 19, 2020 at 01:00:39PM -0800, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@...radead.org>
>
> This series adds a readahead address_space operation to eventually
> replace the readpages operation. The key difference is that
> pages are added to the page cache as they are allocated (and
> then looked up by the filesystem) instead of passing them on a
> list to the readpages operation and having the filesystem add
> them to the page cache. It's a net reduction in code for each
> implementation, more efficient than walking a list, and solves
> the direct-write vs buffered-read problem reported by yu kuai at
> https://lore.kernel.org/linux-fsdevel/20200116063601.39201-1-yukuai3@huawei.com/
>
> The only unconverted filesystems are those which use fscache.
> Their conversion is pending Dave Howells' rewrite which will make the
> conversion substantially easier.
>
> I want to thank the reviewers; Dave Chinner, John Hubbard and Christoph
> Hellwig have done a marvellous job of providing constructive criticism.
> Eric Biggers pointed out how I'd broken ext4 (which led to a substantial
> change). I've tried to take it all on board, but I may have missed
> something simply because you've done such a thorough job.
>
> This series can also be found at
> http://git.infradead.org/users/willy/linux-dax.git/shortlog/refs/tags/readahead_v7
> (I also pushed the readahead_v6 tag there in case anyone wants to diff, and
> they're both based on 5.6-rc2 so they're easy to diff)
>
> v7:
> - Now passes an xfstests run on ext4!
On btrfs it still chokes on the first test btrfs/001, with the following
warning, the test is stuck there.
[ 21.100922] WARNING: suspicious RCU usage
[ 21.103107] 5.6.0-rc2-default+ #996 Not tainted
[ 21.105133] -----------------------------
[ 21.106864] include/linux/xarray.h:1164 suspicious rcu_dereference_check() usage!
[ 21.109948]
[ 21.109948] other info that might help us debug this:
[ 21.109948]
[ 21.113373]
[ 21.113373] rcu_scheduler_active = 2, debug_locks = 1
[ 21.115801] 4 locks held by umount/793:
[ 21.117135] #0: ffff964a736890e8 (&type->s_umount_key#26){+.+.}, at: deactivate_super+0x2f/0x40
[ 21.120188] #1: ffff964a7347ba68 (&delayed_node->mutex){+.+.}, at: __btrfs_commit_inode_delayed_items+0x44c/0x4e0 [btrfs]
[ 21.123042] #2: ffff964a612fe5c8 (&space_info->groups_sem){++++}, at: find_free_extent+0x27d/0xf00 [btrfs]
[ 21.126068] #3: ffff964a60b93280 (&caching_ctl->mutex){+.+.}, at: btrfs_cache_block_group+0x1f0/0x500 [btrfs]
[ 21.129655]
[ 21.129655] stack backtrace:
[ 21.131943] CPU: 1 PID: 793 Comm: umount Not tainted 5.6.0-rc2-default+ #996
[ 21.134164] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.0-59-gc9ba527-rebuilt.opensuse.org 04/01/2014
[ 21.138076] Call Trace:
[ 21.139441] dump_stack+0x71/0xa0
[ 21.140954] xas_start+0x1a4/0x240
[ 21.142473] xas_load+0xa/0x50
[ 21.143874] xas_find+0x226/0x280
[ 21.145298] extent_readahead+0xcb/0x4f0 [btrfs]
[ 21.146934] ? mem_cgroup_commit_charge+0x56/0x400
[ 21.148654] ? rcu_read_lock_sched_held+0x5d/0x90
[ 21.150382] ? __add_to_page_cache_locked+0x327/0x380
[ 21.152155] read_pages+0x80/0x1f0
[ 21.153531] page_cache_readahead_unbounded+0x1b7/0x210
[ 21.155196] __load_free_space_cache+0x1c1/0x730 [btrfs]
[ 21.157014] load_free_space_cache+0xb9/0x190 [btrfs]
[ 21.158222] btrfs_cache_block_group+0x1f8/0x500 [btrfs]
[ 21.159717] ? finish_wait+0x90/0x90
[ 21.160723] find_free_extent+0xa17/0xf00 [btrfs]
[ 21.161798] ? kvm_sched_clock_read+0x14/0x30
[ 21.163022] ? sched_clock_cpu+0x10/0x120
[ 21.164361] btrfs_reserve_extent+0x9b/0x180 [btrfs]
[ 21.165952] btrfs_alloc_tree_block+0xc1/0x350 [btrfs]
[ 21.167680] ? __lock_acquire+0x272/0x1320
[ 21.169353] alloc_tree_block_no_bg_flush+0x4a/0x60 [btrfs]
[ 21.171313] __btrfs_cow_block+0x143/0x7a0 [btrfs]
[ 21.173080] btrfs_cow_block+0x15f/0x310 [btrfs]
[ 21.174487] btrfs_search_slot+0x93b/0xf70 [btrfs]
[ 21.175940] btrfs_lookup_inode+0x3a/0xc0 [btrfs]
[ 21.177419] ? __btrfs_commit_inode_delayed_items+0x417/0x4e0 [btrfs]
[ 21.179032] ? __btrfs_commit_inode_delayed_items+0x44c/0x4e0 [btrfs]
[ 21.180787] __btrfs_update_delayed_inode+0x73/0x260 [btrfs]
[ 21.182174] __btrfs_commit_inode_delayed_items+0x46c/0x4e0 [btrfs]
[ 21.183907] ? btrfs_first_delayed_node+0x4c/0x90 [btrfs]
[ 21.185204] __btrfs_run_delayed_items+0x8e/0x140 [btrfs]
[ 21.186521] btrfs_commit_transaction+0x312/0xae0 [btrfs]
[ 21.188142] ? btrfs_attach_transaction_barrier+0x1f/0x50 [btrfs]
[ 21.189684] sync_filesystem+0x6e/0x90
[ 21.190878] generic_shutdown_super+0x22/0x100
[ 21.192693] kill_anon_super+0x14/0x30
[ 21.194389] btrfs_kill_super+0x12/0x20 [btrfs]
[ 21.196078] deactivate_locked_super+0x2c/0x70
[ 21.197732] cleanup_mnt+0x100/0x160
[ 21.199033] task_work_run+0x90/0xc0
[ 21.200331] exit_to_usermode_loop+0x96/0xa0
[ 21.201744] do_syscall_64+0x1df/0x210
[ 21.203187] entry_SYSCALL_64_after_hwframe+0x49/0xbe
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