linux-ext4 - Re: [PATCH v6 00/19] Change readahead API

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Message-ID: <20200218045633.GH10776@dread.disaster.area>
Date:   Tue, 18 Feb 2020 15:56:33 +1100
From:   Dave Chinner <david@...morbit.com>
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 v6 00/19] Change readahead API

On Mon, Feb 17, 2020 at 10:45:41AM -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.

Latest version in your git tree:

$ ▶ glo -n 5 willy/readahead
4be497096c04 mm: Use memalloc_nofs_save in readahead path
ff63497fcb98 iomap: Convert from readpages to readahead
26aee60e89b5 iomap: Restructure iomap_readpages_actor
8115bcca7312 fuse: Convert from readpages to readahead
3db3d10d9ea1 f2fs: Convert from readpages to readahead
$

merged into a 5.6-rc2 tree fails at boot on my test vm:

[    2.423116] ------------[ cut here ]------------
[    2.424957] list_add double add: new=ffffea000efff4c8, prev=ffff8883bfffee60, next=ffffea000efff4c8.
[    2.428259] WARNING: CPU: 4 PID: 1 at lib/list_debug.c:29 __list_add_valid+0x67/0x70
[    2.430617] CPU: 4 PID: 1 Comm: sh Not tainted 5.6.0-rc2-dgc+ #1800
[    2.432405] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-1 04/01/2014
[    2.434744] RIP: 0010:__list_add_valid+0x67/0x70
[    2.436107] Code: c6 4c 89 ca 48 c7 c7 10 41 58 82 e8 55 29 89 ff 0f 0b 31 c0 c3 48 89 f2 4c 89 c1 48 89 fe 48 c7 c7 60 41 58 82 e8 3b 29 89 ff <0f> 0b 31 c7
[    2.441161] RSP: 0000:ffffc900018a3bb0 EFLAGS: 00010082
[    2.442548] RAX: 0000000000000000 RBX: ffffea000efff4c0 RCX: 0000000000000256
[    2.444432] RDX: 0000000000000001 RSI: 0000000000000086 RDI: ffffffff8288a8b0
[    2.446315] RBP: ffffea000efff4c8 R08: ffffc900018a3a65 R09: 0000000000000256
[    2.448199] R10: 0000000000000008 R11: ffffc900018a3a65 R12: ffffea000efff4c8
[    2.450072] R13: ffff8883bfffee60 R14: 0000000000000010 R15: 0000000000000001
[    2.451959] FS:  0000000000000000(0000) GS:ffff8883b9c00000(0000) knlGS:0000000000000000
[    2.454083] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[    2.455604] CR2: 00000000ffffffff CR3: 00000003b9a37002 CR4: 0000000000060ee0
[    2.457484] Call Trace:
[    2.458171]  __pagevec_lru_add_fn+0x15f/0x2c0
[    2.459376]  pagevec_lru_move_fn+0x87/0xd0
[    2.460500]  ? pagevec_move_tail_fn+0x2d0/0x2d0
[    2.461712]  lru_add_drain_cpu+0x8d/0x160
[    2.462787]  lru_add_drain+0x18/0x20
[    2.463757]  shift_arg_pages+0xb8/0x180
[    2.464789]  ? vprintk_emit+0x101/0x1c0
[    2.465813]  ? printk+0x58/0x6f
[    2.466659]  setup_arg_pages+0x205/0x240
[    2.467716]  load_elf_binary+0x34a/0x1560
[    2.468789]  ? get_user_pages_remote+0x159/0x280
[    2.470024]  ? selinux_inode_permission+0x10d/0x1e0
[    2.471323]  ? _raw_read_unlock+0xa/0x20
[    2.472375]  ? load_misc_binary+0x2b2/0x410
[    2.473492]  search_binary_handler+0x60/0xe0
[    2.474634]  __do_execve_file.isra.0+0x512/0x850
[    2.475888]  ? rest_init+0xc6/0xc6
[    2.476801]  do_execve+0x21/0x30
[    2.477671]  try_to_run_init_process+0x10/0x34
[    2.478855]  kernel_init+0xe2/0xfa
[    2.479776]  ret_from_fork+0x1f/0x30
[    2.480737] ---[ end trace e77079de9b22dc6a ]---

I just dropped the ext4 conversion from my local tree so I can boot
the machine and test XFS. Might have some more info when that
crashes and burns...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com