Re: [PATCH v5 2/2] btrfs: Don't block system suspend during fstrim

[David Sterba <dsterba@suse.cz>]

On Mon, Sep 16, 2024 at 02:56:15PM +0200, Luca Stefani wrote:
> Sometimes the system isn't able to suspend because the task
> responsible for trimming the device isn't able to finish in
> time, especially since 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).
> 
> Since discard isn't a critical call it can be interrupted
> at any time, in such cases we stop the trim, report the amount
> of discarded bytes and return failure.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=219180
> Link: https://bugzilla.suse.com/show_bug.cgi?id=1229737
> Signed-off-by: Luca Stefani <luca.stefani.ge1@gmail.com>

I went through the cancellation points, some of them don't seem to be
necessary, eg. in a big loop when some function is called to do trim
(extents, bitmaps) and then again does the signal and freezing check.

Next, some of the functions are called from async discard and errors are
not checked: btrfs_trim_block_group_bitmaps() called from
btrfs_discard_workfn().

Ther's also check for signals pending in trim_bitmaps() in
free-space-cache.c. Given that the space cache code is on the way out we
don't necesssarily need to fix it but if the patch gets backported to
older kernels it still makes sense.

> ---
>  fs/btrfs/extent-tree.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 79b9243c9cd6..cef368a30731 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"
> @@ -1235,6 +1236,11 @@ static int remove_extent_backref(struct btrfs_trans_handle *trans,
>  	return ret;
>  }
>  
> +static bool btrfs_trim_interrupted(void)
> +{
> +	return fatal_signal_pending(current) || freezing(current);
> +}
> +
>  static int btrfs_issue_discard(struct block_device *bdev, u64 start, u64 len,
>  			       u64 *discarded_bytes)
>  {
> @@ -1316,6 +1322,11 @@ static int btrfs_issue_discard(struct block_device *bdev, u64 start, u64 len,
>  		start += bytes_to_discard;
>  		bytes_left -= bytes_to_discard;
>  		*discarded_bytes += bytes_to_discard;
> +
> +		if (btrfs_trim_interrupted()) {
> +			ret = -ERESTARTSYS;
> +			break;
> +		}
>  	}
>  
>  	return ret;
> @@ -6470,7 +6481,7 @@ static int btrfs_trim_free_extents(struct btrfs_device *device, u64 *trimmed)
>  		start += len;
>  		*trimmed += bytes;
>  
> -		if (fatal_signal_pending(current)) {
> +		if (btrfs_trim_interrupted()) {
>  			ret = -ERESTARTSYS;
>  			break;
>  		}
> @@ -6519,6 +6530,11 @@ 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()) {
> +			bg_ret = -ERESTARTSYS;
> +			break;
> +		}
> +
>  		if (cache->start >= range_end) {
>  			btrfs_put_block_group(cache);
>  			break;
> @@ -6558,6 +6574,11 @@ 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()) {
> +			dev_ret = -ERESTARTSYS;

This one seems redundant.

> +			break;
> +		}
> +
>  		if (test_bit(BTRFS_DEV_STATE_MISSING, &device->dev_state))
>  			continue;
>  
> -- 
> 2.46.0
>