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

[Luca Stefani]

On 17/09/24 18:24, David Sterba wrote:
> 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@xxxxxxxxx>
>
> 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().
Both btrfs_trim_block_group_bitmaps and btrfs_trim_block_group_extents 
ret codes are never checked indeed in btrfs_discard_workfn. I'll fix 
that up in another CL.
> 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.
Ah I missed this one, will fix it.
There's a few more instances of fatal_signal_pending but I don't know if 
they should be translated or not, will focus on the one you mentioned 
and trim_no_bitmap which seems to do similar checks for fatal signals.
> > ---
> >   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