[PATCH 0/2] btrfs: scrub: update last_physical more frequently

[PATCH 0/2] btrfs: scrub: update last_physical more frequently

[Qu Wenruo]

There is a report in the mailling list that scrub only updates its
@last_physical at the end of a chunk.
In fact, it can be worse if there is a used stripe (aka, some extents
exist in the stripe) at the chunk boundary.
As it would skip the @last_physical for that chunk at all.

With @last_physical not update for a long time, if we cancel the scrub
halfway and resume, the resumed one scrub would only start at
@last_physical, meaning a lot of scrubbed extents would be re-scrubbed,
wasting quite some IO and CPU.

This patchset would fix it by updateing @last_physical for each finished
stripe (including both P/Q stripe of RAID56, and all data stripes for
all profiles), so that even if the scrub is cancelled, we at most
re-scrub one stripe.

Qu Wenruo (2):
  btrfs: extract the stripe length calculation into a helper
  btrfs: scrub: update last_physical after scrubing one stripe

 fs/btrfs/scrub.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

-- 
2.44.0

[PATCH 0/2] btrfs: scrub: update last_physical more frequently

[Qu Wenruo]

There is a report in the mailling list that scrub only updates its
@last_physical at the end of a chunk.
In fact, it can be worse if there is a used stripe (aka, some extents
exist in the stripe) at the chunk boundary.
As it would skip the @last_physical for that chunk at all.

With @last_physical not update for a long time, if we cancel the scrub
halfway and resume, the resumed one scrub would only start at
@last_physical, meaning a lot of scrubbed extents would be re-scrubbed,
wasting quite some IO and CPU.

This patchset would fix it by updateing @last_physical for each finished
stripe (including both P/Q stripe of RAID56, and all data stripes for
all profiles), so that even if the scrub is cancelled, we at most
re-scrub one stripe.

Qu Wenruo (2):
  btrfs: extract the stripe length calculation into a helper
  btrfs: scrub: update last_physical after scrubing one stripe

 fs/btrfs/scrub.c | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

-- 
2.44.0

[PATCH 1/2] btrfs: extract the stripe length calculation into a helper

[Qu Wenruo]

Currently there are two location which needs to calculate the real
length of a stripe (which can be at the end of a chunk, and the chunk
size may not always be 64K aligned).

Extract them into a helper as we're going to have a third user soon.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/scrub.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index c4bd0e60db59..8a21214eca35 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1648,14 +1648,21 @@ static void scrub_reset_stripe(struct scrub_stripe *stripe)
 	}
 }
 
+static u32 stripe_length(struct scrub_stripe *stripe)
+{
+	ASSERT(stripe->bg);
+
+	return min(BTRFS_STRIPE_LEN,
+		   stripe->bg->start + stripe->bg->length - stripe->logical);
+
+}
+
 static void scrub_submit_extent_sector_read(struct scrub_ctx *sctx,
 					    struct scrub_stripe *stripe)
 {
 	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
 	struct btrfs_bio *bbio = NULL;
-	unsigned int nr_sectors = min(BTRFS_STRIPE_LEN, stripe->bg->start +
-				      stripe->bg->length - stripe->logical) >>
-				  fs_info->sectorsize_bits;
+	unsigned int nr_sectors = stripe_length(stripe) >> fs_info->sectorsize_bits;
 	u64 stripe_len = BTRFS_STRIPE_LEN;
 	int mirror = stripe->mirror_num;
 	int i;
@@ -1725,9 +1732,7 @@ static void scrub_submit_initial_read(struct scrub_ctx *sctx,
 {
 	struct btrfs_fs_info *fs_info = sctx->fs_info;
 	struct btrfs_bio *bbio;
-	unsigned int nr_sectors = min(BTRFS_STRIPE_LEN, stripe->bg->start +
-				      stripe->bg->length - stripe->logical) >>
-				  fs_info->sectorsize_bits;
+	unsigned int nr_sectors = stripe_length(stripe) >> fs_info->sectorsize_bits;
 	int mirror = stripe->mirror_num;
 
 	ASSERT(stripe->bg);
-- 
2.44.0

[PATCH 1/2] btrfs: extract the stripe length calculation into a helper

[Qu Wenruo]

Currently there are two location which needs to calculate the real
length of a stripe (which can be at the end of a chunk, and the chunk
size may not always be 64K aligned).

Extract them into a helper as we're going to have a third user soon.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/scrub.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index c4bd0e60db59..8a21214eca35 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1648,14 +1648,21 @@ static void scrub_reset_stripe(struct scrub_stripe *stripe)
 	}
 }
 
+static u32 stripe_length(struct scrub_stripe *stripe)
+{
+	ASSERT(stripe->bg);
+
+	return min(BTRFS_STRIPE_LEN,
+		   stripe->bg->start + stripe->bg->length - stripe->logical);
+
+}
+
 static void scrub_submit_extent_sector_read(struct scrub_ctx *sctx,
 					    struct scrub_stripe *stripe)
 {
 	struct btrfs_fs_info *fs_info = stripe->bg->fs_info;
 	struct btrfs_bio *bbio = NULL;
-	unsigned int nr_sectors = min(BTRFS_STRIPE_LEN, stripe->bg->start +
-				      stripe->bg->length - stripe->logical) >>
-				  fs_info->sectorsize_bits;
+	unsigned int nr_sectors = stripe_length(stripe) >> fs_info->sectorsize_bits;
 	u64 stripe_len = BTRFS_STRIPE_LEN;
 	int mirror = stripe->mirror_num;
 	int i;
@@ -1725,9 +1732,7 @@ static void scrub_submit_initial_read(struct scrub_ctx *sctx,
 {
 	struct btrfs_fs_info *fs_info = sctx->fs_info;
 	struct btrfs_bio *bbio;
-	unsigned int nr_sectors = min(BTRFS_STRIPE_LEN, stripe->bg->start +
-				      stripe->bg->length - stripe->logical) >>
-				  fs_info->sectorsize_bits;
+	unsigned int nr_sectors = stripe_length(stripe) >> fs_info->sectorsize_bits;
 	int mirror = stripe->mirror_num;
 
 	ASSERT(stripe->bg);
-- 
2.44.0

Re: [PATCH 1/2] btrfs: extract the stripe length calculation into a helper

[Johannes Thumshirn]

Looks good,
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>

[PATCH 2/2] btrfs: scrub: update last_physical after scrubing one stripe

[Qu Wenruo]

Currently sctx->stat.last_physical only got updated in the following
cases:

- When the last stripe of a non-RAID56 chunk is scrubbed
  This implies a pitfall, if the last stripe is at the chunk boundary,
  and we finished the scrub of the whole chunk, we won't update
  last_physical at all until the next chunk.

- When a P/Q stripe of a RAID56 chunk is scrubbed

This leads makes sctx->stat.last_physical to be not update for a long
time if we're scrubbing a large data chunk (which can go up to 10GiB).

And if scrub is cancelled halfway, we would restart from last_physical,
but that last_physical is only updated to the last finished chunk end,
we would re-scrub the same chunk again.

This can waste a lot of time especially when the chunk is huge.

Fix the problem by properly updating @last_physical after each stripe is
scrubbed.

And since we're here, for the sake of consistency, use spin lock to
protect the update of @last_physical, just like all the remaining
call sites touching sctx->stat.

Reported-by: Michel Palleau <michel.palleau@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CAMFk-+igFTv2E8svg=cQ6o3e6CrR5QwgQ3Ok9EyRaEvvthpqCQ@mail.gmail.com/
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/scrub.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 8a21214eca35..3bccd171be61 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1872,6 +1872,8 @@ static int flush_scrub_stripes(struct scrub_ctx *sctx)
 		stripe = &sctx->stripes[i];
 
 		wait_scrub_stripe_io(stripe);
+		sctx->stat.last_physical = stripe->physical +
+					   stripe_length(stripe);
 		scrub_reset_stripe(stripe);
 	}
 out:
@@ -2337,6 +2339,8 @@ static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
 			stripe_logical += chunk_logical;
 			ret = scrub_raid56_parity_stripe(sctx, scrub_dev, bg,
 							 map, stripe_logical);
+			sctx->stat.last_physical = min(physical + BTRFS_STRIPE_LEN,
+						       physical_end);
 			if (ret)
 				goto out;
 			goto next;
-- 
2.44.0

[PATCH 2/2] btrfs: scrub: update last_physical after scrubing one stripe

[Qu Wenruo]

Currently sctx->stat.last_physical only got updated in the following
cases:

- When the last stripe of a non-RAID56 chunk is scrubbed
  This implies a pitfall, if the last stripe is at the chunk boundary,
  and we finished the scrub of the whole chunk, we won't update
  last_physical at all until the next chunk.

- When a P/Q stripe of a RAID56 chunk is scrubbed

This leads makes sctx->stat.last_physical to be not update for a long
time if we're scrubbing a large data chunk (which can go up to 10GiB).

And if scrub is cancelled halfway, we would restart from last_physical,
but that last_physical is only updated to the last finished chunk end,
we would re-scrub the same chunk again.

This can waste a lot of time especially when the chunk is huge.

Fix the problem by properly updating @last_physical after each stripe is
scrubbed.

And since we're here, for the sake of consistency, use spin lock to
protect the update of @last_physical, just like all the remaining
call sites touching sctx->stat.

Reported-by: Michel Palleau <michel.palleau@gmail.com>
Link: https://lore.kernel.org/linux-btrfs/CAMFk-+igFTv2E8svg=cQ6o3e6CrR5QwgQ3Ok9EyRaEvvthpqCQ@mail.gmail.com/
Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/scrub.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/btrfs/scrub.c b/fs/btrfs/scrub.c
index 8a21214eca35..3bccd171be61 100644
--- a/fs/btrfs/scrub.c
+++ b/fs/btrfs/scrub.c
@@ -1872,6 +1872,8 @@ static int flush_scrub_stripes(struct scrub_ctx *sctx)
 		stripe = &sctx->stripes[i];
 
 		wait_scrub_stripe_io(stripe);
+		sctx->stat.last_physical = stripe->physical +
+					   stripe_length(stripe);
 		scrub_reset_stripe(stripe);
 	}
 out:
@@ -2337,6 +2339,8 @@ static noinline_for_stack int scrub_stripe(struct scrub_ctx *sctx,
 			stripe_logical += chunk_logical;
 			ret = scrub_raid56_parity_stripe(sctx, scrub_dev, bg,
 							 map, stripe_logical);
+			sctx->stat.last_physical = min(physical + BTRFS_STRIPE_LEN,
+						       physical_end);
 			if (ret)
 				goto out;
 			goto next;
-- 
2.44.0

Re: [PATCH 0/2] btrfs: scrub: update last_physical more frequently

[Qu Wenruo]

Ping?

Any feedback on this small series?

Thanks,
Qu

在 2024/3/8 13:55, Qu Wenruo 写道:
> There is a report in the mailling list that scrub only updates its
> @last_physical at the end of a chunk.
> In fact, it can be worse if there is a used stripe (aka, some extents
> exist in the stripe) at the chunk boundary.
> As it would skip the @last_physical for that chunk at all.
> 
> With @last_physical not update for a long time, if we cancel the scrub
> halfway and resume, the resumed one scrub would only start at
> @last_physical, meaning a lot of scrubbed extents would be re-scrubbed,
> wasting quite some IO and CPU.
> 
> This patchset would fix it by updateing @last_physical for each finished
> stripe (including both P/Q stripe of RAID56, and all data stripes for
> all profiles), so that even if the scrub is cancelled, we at most
> re-scrub one stripe.
> 
> Qu Wenruo (2):
>    btrfs: extract the stripe length calculation into a helper
>    btrfs: scrub: update last_physical after scrubing one stripe
> 
>   fs/btrfs/scrub.c | 21 +++++++++++++++------
>   1 file changed, 15 insertions(+), 6 deletions(-)
>