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Message-ID: <22c49ecd-e268-4738-853e-9f79ea1e87f7@gmx.com>
Date: Mon, 2 Sep 2024 18:42:34 +0930
From: Qu Wenruo <quwenruo.btrfs@....com>
To: Luca Stefani <luca.stefani.ge1@...il.com>
Cc: Chris Mason <clm@...com>, Josef Bacik <josef@...icpanda.com>,
David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] btrfs: Don't block system suspend during fstrim
在 2024/9/2 18:30, Luca Stefani 写道:
>
>
> On Mon, 2 Sept 2024 at 10:49, Qu Wenruo <quwenruo.btrfs@....com
> <mailto:quwenruo.btrfs@....com>> wrote:
>
>
>
> 在 2024/9/2 18:02, Luca Stefani 写道:
> > Any update on this? It's not critical but I'd like to know if it's in
> > some part proper.
> > Thanks, Luca.
>
> Sorry I didn't see your patch in the list, thus sent a different fix for
> it later:
>
> https://lore.kernel.org/linux-btrfs/20240830185113.GW25962@twin.jikos.cz/T/#t <https://lore.kernel.org/linux-btrfs/20240830185113.GW25962@twin.jikos.cz/T/#t>
>
> >> Sometimes the system isn't able to suspend because
> >> the task responsible for trimming the device isn't
> >> able to finish in time.
> >>
> >> Since discard isn't a critical call it can be interrupted
> >> at any time, we can simply report the amount of discarded
> >> bytes in such cases and stop the trim.
> >>
> >> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219180
> <https://bugzilla.kernel.org/show_bug.cgi?id=219180>
> >> Signed-off-by: Luca Stefani <luca.stefani.ge1@...il.com
> <mailto:luca.stefani.ge1@...il.com>>
> >> ---
> >> I have no idea if that's correct, just something I implemented
> >> looking at the same solution made in ext4 by 5229a658f645.
> >>
> >> The patch in itself seems to solve the issue.
> >>
> >> repro is as follows:
> >> sudo /sbin/fstrim --listed-in /etc/fstab:/proc/self/mountinfo
> >> --verbose --quiet-unsupported &
> >> sudo ./sleepgraph.py -m mem -rtcwake 5
> >>
> >> [836563.289069] PM: suspend exit
> >> [836563.909298] PM: suspend entry (s2idle)
> >> [836563.935447] Filesystems sync: 0.026 seconds
> >> [836563.951391] Freezing user space processes
> >> [836583.958957] Freezing user space processes failed after 20.007
> >> seconds (1 tasks refusing to freeze, wq_busy=0):
> >> [836583.959582] task:fstrim state:D stack:0 pid:241865
> >> tgid:241865 ppid:241864 flags:0x00004006
> >> [836583.959592] Call Trace:
> >> [836583.959595] <TASK>
> >> [836583.959600] __schedule+0x400/0x1720
> >> [836583.959612] ? mod_delayed_work_on+0xa4/0xb0
> >> [836583.959622] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959628] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959631] ? blk_mq_flush_plug_list.part.0+0x1e3/0x610
> >> [836583.959640] schedule+0x27/0xf0
> >> [836583.959644] schedule_timeout+0x12f/0x160
> >> [836583.959652] io_schedule_timeout+0x51/0x70
> >> [836583.959657] wait_for_completion_io+0x8a/0x160
> >> [836583.959663] submit_bio_wait+0x60/0x90
> >> [836583.959671] blkdev_issue_discard+0x91/0x100
> >> [836583.959680] btrfs_issue_discard+0xc4/0x140
> >> [836583.959689] btrfs_discard_extent+0x241/0x2a0
> >> [836583.959695] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959702] do_trimming+0xd2/0x240
> >> [836583.959712] trim_bitmaps+0x350/0x4c0
> >> [836583.959723] btrfs_trim_block_group+0xb8/0x110
> >> [836583.959729] btrfs_trim_fs+0x118/0x440
> >> [836583.959734] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959738] ? security_capable+0x41/0x70
> >> [836583.959746] btrfs_ioctl_fitrim+0x113/0x180
> >> [836583.959752] btrfs_ioctl+0xdaf/0x2670
> >> [836583.959759] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959763] ? ioctl_has_perm.constprop.0.isra.0+0xd8/0x130
> >> [836583.959774] __x64_sys_ioctl+0x94/0xd0
> >> [836583.959782] do_syscall_64+0x82/0x160
> >> [836583.959790] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959793] ? syscall_exit_to_user_mode+0x72/0x220
> >> [836583.959799] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959802] ? do_syscall_64+0x8e/0x160
> >> [836583.959807] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959811] ? do_sys_openat2+0x9c/0xe0
> >> [836583.959821] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959825] ? syscall_exit_to_user_mode+0x72/0x220
> >> [836583.959828] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959832] ? do_syscall_64+0x8e/0x160
> >> [836583.959835] ? syscall_exit_to_user_mode+0x72/0x220
> >> [836583.959838] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959842] ? do_syscall_64+0x8e/0x160
> >> [836583.959845] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959849] ? do_syscall_64+0x8e/0x160
> >> [836583.959851] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959855] ? do_syscall_64+0x8e/0x160
> >> [836583.959858] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959861] ? do_syscall_64+0x8e/0x160
> >> [836583.959864] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959868] ? srso_alias_return_thunk+0x5/0xfbef5
> >> [836583.959873] entry_SYSCALL_64_after_hwframe+0x76/0x7e
> >> [836583.959878] RIP: 0033:0x7f3e4261af2d
> >> [836583.959944] RSP: 002b:00007ffec002f400 EFLAGS: 00000246
> ORIG_RAX:
> >> 0000000000000010
> >> [836583.959950] RAX: ffffffffffffffda RBX: 00007ffec002f570 RCX:
> >> 00007f3e4261af2d
> >> [836583.959952] RDX: 00007ffec002f470 RSI: 00000000c0185879 RDI:
> >> 0000000000000003
> >> [836583.959955] RBP: 00007ffec002f450 R08: 0000562d74da7010 R09:
> >> 00007ffec002e7f2
> >> [836583.959957] R10: 0000000000000000 R11: 0000000000000246 R12:
> >> 0000562d74daafc0
> >> [836583.959960] R13: 0000000000000003 R14: 0000562d74daa970 R15:
> >> 0000562d74daad40
> >> [836583.959967] </TASK>
> >> ---
> >> fs/btrfs/extent-tree.c | 20 ++++++++++++++++----
> >> 1 file changed, 16 insertions(+), 4 deletions(-)
> >>
> >> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> >> index feec49e6f9c8..7e4c1d4f2f7c 100644
> >> --- a/fs/btrfs/extent-tree.c
> >> +++ b/fs/btrfs/extent-tree.c
> >> @@ -16,6 +16,7 @@
> >> #include <linux/percpu_counter.h>
> >> #include <linux/lockdep.h>
> >> #include <linux/crc32c.h>
> >> +#include <linux/freezer.h>
> >> #include "ctree.h"
> >> #include "extent-tree.h"
> >> #include "transaction.h"
> >> @@ -6361,6 +6362,11 @@ void btrfs_error_unpin_extent_range(struct
> >> btrfs_fs_info *fs_info, u64 start, u6
> >> unpin_extent_range(fs_info, start, end, false);
> >> }
> >> +static bool btrfs_trim_interrupted(void)
> >> +{
> >> + return fatal_signal_pending(current) || freezing(current);
> >> +}
> >> +
> >> /*
> >> * It used to be that old block groups would be left around
> forever.
> >> * Iterating over them would be enough to trim unused space.
> Since we
> >> @@ -6459,8 +6465,8 @@ static int btrfs_trim_free_extents(struct
> >> btrfs_device *device, u64 *trimmed)
> >> start += len;
> >> *trimmed += bytes;
> >> - if (fatal_signal_pending(current)) {
> >> - ret = -ERESTARTSYS;
> >> + if (btrfs_trim_interrupted()) {
> >> + ret = 0;
> >> break;
>
> Here we should still return the same error number other than 0, to let
> the caller know the operation is interrupted, other than finished
> normally.
>
> Here I was following how ext4 did it, my explanation for that was that
> the kernel
> may have still discarded some data before the thread was interrupted
> thus it made
> sense to report success.
In that case, progress is reported through fstrim_range structure, not
through the return value.
Even if we returned some error code, the fstrim_range::len is still
updated to indicate the progress.
So we need to keep the error code.
>
>
> >> }
> >> @@ -6508,6 +6514,9 @@ int btrfs_trim_fs(struct btrfs_fs_info
> *fs_info,
> >> struct fstrim_range *range)
> >> cache = btrfs_lookup_first_block_group(fs_info, range->start);
> >> for (; cache; cache = btrfs_next_block_group(cache)) {
> >> + if (btrfs_trim_interrupted())
> >> + break;
> >> +
>
> The same here.
>
> >> if (cache->start >= range_end) {
> >> btrfs_put_block_group(cache);
> >> break;
> >> @@ -6547,17 +6556,20 @@ int btrfs_trim_fs(struct btrfs_fs_info
> >> *fs_info, struct fstrim_range *range)
> >> mutex_lock(&fs_devices->device_list_mutex);
> >> list_for_each_entry(device, &fs_devices->devices, dev_list) {
> >> + if (btrfs_trim_interrupted())
> >> + break;
> >> +
>
> The same here.
>
> Furthermore, I think we may not need the extra checks.
>
> The fstrim is based on block groups, and a block group is normally 1GiB,
> at most 10GiB (for RAID0/5/6/10 only), thus exiting at each block group
> boundary should be enough to meet the hibernation/suspension timeout.
>
> That's probably true, but 10seconds here wasn't enough and forcing the
> early return in the other cases
> was also required.
> I tried the current patch you linked earlier in my testing and that was
> the conclusion that led to me adding more checks.
My bad, I forgot that we have free extents trimming, which is not
limited to block group boundary, and that may be the root cause.
So in that case your extra checks are indeed needed.
Just need to change the return value.
>
>
>
>
> >> if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
> >> continue;
> >> ret = btrfs_trim_free_extents(device, &group_trimmed);
> >> +
> >> + trimmed += group_trimmed;
> >> if (ret) {
> >> dev_failed++;
> >> dev_ret = ret;
> >> break;
> >> }
> >> -
> >> - trimmed += group_trimmed;
>
> Any special reason moving the code here?
>
> Same as not returning errno before in case of interrupt, I checked the
> code paths and it's still
> possible to trim some data (group_trimmed != 0) even in case of failure.
Oh, then it's fine.
Except the return code, everything looks fine to me now.
Just please update the commit message to explicitly mention that, we
have a free extent discarding phase, which can trim a lot of unallocated
space, and there is no limits on the trim size (unlike the block group
part).
Thanks,
Qu
>
> Thanks,
> Qu
>
> >> }
> >> mutex_unlock(&fs_devices->device_list_mutex);
> >
>
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