* [PATCH] btrfs: raid56: do blk_check_plugged check twice while writing
@ 2022-03-19 1:18 Yusuf Khan
2022-03-19 18:31 ` Sweet Tea Dorminy
0 siblings, 1 reply; 2+ messages in thread
From: Yusuf Khan @ 2022-03-19 1:18 UTC (permalink / raw)
To: linux-btrfs; +Cc: linux-kernel, dsterba, josef, clm, Yusuf Khan
Do the check to see if the drive was connected twice in case that
the first was a fluke.
Signed-off-by: Yusuf Khan <yusisamerican@gmail.com>
---
fs/btrfs/raid56.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)
diff --git a/fs/btrfs/raid56.c b/fs/btrfs/raid56.c
index 0e239a4c3b26..f652900d7569 100644
--- a/fs/btrfs/raid56.c
+++ b/fs/btrfs/raid56.c
@@ -1750,18 +1750,23 @@ int raid56_parity_write(struct bio *bio, struct btrfs_io_context *bioc,
cb = blk_check_plugged(btrfs_raid_unplug, fs_info, sizeof(*plug));
if (cb) {
- plug = container_of(cb, struct btrfs_plug_cb, cb);
- if (!plug->info) {
- plug->info = fs_info;
- INIT_LIST_HEAD(&plug->rbio_list);
+ cpu_relax();
+ cb = blk_check_plugged(btrfs_raid_unplug, fs_info, sizeof(*plug));
+ if (cb) {
+ plug = container_of(cb, struct btrfs_plug_cb, cb);
+ if (!plug->info) {
+ plug->info = fs_info;
+ INIT_LIST_HEAD(&plug->rbio_list);
+ }
+ list_add_tail(&rbio->plug_list, &plug->rbio_list);
+ return 0;
}
- list_add_tail(&rbio->plug_list, &plug->rbio_list);
- ret = 0;
- } else {
- ret = __raid56_parity_write(rbio);
- if (ret)
- btrfs_bio_counter_dec(fs_info);
+ btrfs_warn(fs_info,
+"during a write operation, the first check to see if the drive was plugged in failed, seccond check succeeded, write continued");
}
+ ret = __raid56_parity_write(rbio);
+ if (ret)
+ btrfs_bio_counter_dec(fs_info);
return ret;
}
--
2.25.1
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] btrfs: raid56: do blk_check_plugged check twice while writing
2022-03-19 1:18 [PATCH] btrfs: raid56: do blk_check_plugged check twice while writing Yusuf Khan
@ 2022-03-19 18:31 ` Sweet Tea Dorminy
0 siblings, 0 replies; 2+ messages in thread
From: Sweet Tea Dorminy @ 2022-03-19 18:31 UTC (permalink / raw)
To: Yusuf Khan, linux-btrfs; +Cc: linux-kernel, dsterba, josef, clm
Hi Yusuf:
On 3/18/22 21:18, Yusuf Khan wrote:
> Do the check to see if the drive was connected twice in case that
> the first was a fluke.
Block plugging is not actually about checking the connectivity of the
drive; it's about batching IO submission. Specifically, when a client of
the block layer (a filesystem or DM device, for instance) knows that it
needs to send a whole batch of IO to disk from a thread, it can request
the thread's be temporarily delayed, with blk_start_plug()
(block/blk-core.c has a lengthy great comment about it). Then it submits
its batch of requests. Finally, it requests the plug be released. This
is useful because it can allow better IO by releasing a large,
potentially better ordered batch at once.
In this particular case, to my understanding, blk_check_plug() checks
whether the current thread is plugged, and, if it is, it adds the rbio
to a list; when the plug expires, perhaps from the thread going to
sleep, the plug callback gets called, specifically btrfs_raid_unplug(),
which sorts the pending IOs.
As such, it shouldn't be necessary to check whether the thread is
plugged twice. Your change description is a little light on *why* you'd
like to check twice; maybe I'm missing something.
Hope this helps,
Sweet Tea
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2022-03-19 1:18 [PATCH] btrfs: raid56: do blk_check_plugged check twice while writing Yusuf Khan
2022-03-19 18:31 ` Sweet Tea Dorminy
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