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

Dave Chinner
2020-02-18T04:56:55Z

On Mon, Feb 17, 2020 at 10:45:41AM -0800, Matthew Wilcox wrote:
> From: "Matthew Wilcox (Oracle)" <willy@infradead.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@fromorbit.com