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xfs: use a seprate member to track space availabe in the GC scatch buffer

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When scratch_head wraps back to 0 and scratch_tail is also 0 because no
I/O has completed yet, the ring buffer could be mistaken for empty.

Fix this by introducing a separate scratch_available member in
struct xfs_zone_gc_data.  This actually ends up simplifying the code as
well.

Reported-by: Chris Mason <clm@meta.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Hans Holmberg <hans.holmberg@wdc.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
This commit is contained in:
Christoph Hellwig 2026-01-27 16:10:20 +01:00 • committed by Carlos Maiolino
parent 692243cac6
commit c17a1c0349
1 changed files with 9 additions and 16 deletions
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25
fs/xfs/xfs_zone_gc.c
View file

@ -131,10 +131,13 @@ struct xfs_zone_gc_data {
/*
* Scratchpad to buffer GC data, organized as a ring buffer over
* discontiguous folios. scratch_head is where the buffer is filled,
* and scratch_tail tracks the buffer space freed.
* scratch_tail tracks the buffer space freed, and scratch_available
* counts the space available in the ring buffer between the head and
* the tail.
*/
struct folio *scratch_folios[XFS_GC_NR_BUFS];
unsigned int scratch_size;
unsigned int scratch_available;
unsigned int scratch_head;
unsigned int scratch_tail;
@ -212,6 +215,7 @@ xfs_zone_gc_data_alloc(
goto out_free_scratch;
}
data->scratch_size = XFS_GC_BUF_SIZE * XFS_GC_NR_BUFS;
data->scratch_available = data->scratch_size;
INIT_LIST_HEAD(&data->reading);
INIT_LIST_HEAD(&data->writing);
INIT_LIST_HEAD(&data->resetting);
@ -574,18 +578,6 @@ xfs_zone_gc_ensure_target(
return oz;
}
static unsigned int
xfs_zone_gc_scratch_available(
struct xfs_zone_gc_data *data)
{
if (!data->scratch_tail)
return data->scratch_size - data->scratch_head;
if (!data->scratch_head)
return data->scratch_tail;
return (data->scratch_size - data->scratch_head) + data->scratch_tail;
}
static bool
xfs_zone_gc_space_available(
struct xfs_zone_gc_data *data)
@ -596,7 +588,7 @@ xfs_zone_gc_space_available(
if (!oz)
return false;
return oz->oz_allocated < rtg_blocks(oz->oz_rtg) &&
xfs_zone_gc_scratch_available(data);
data->scratch_available;
}
static void
@ -625,8 +617,7 @@ xfs_zone_gc_alloc_blocks(
if (!oz)
return NULL;
*count_fsb = min(*count_fsb,
XFS_B_TO_FSB(mp, xfs_zone_gc_scratch_available(data)));
*count_fsb = min(*count_fsb, XFS_B_TO_FSB(mp, data->scratch_available));
/*
* Directly allocate GC blocks from the reserved pool.
@ -730,6 +721,7 @@ xfs_zone_gc_start_chunk(
bio->bi_end_io = xfs_zone_gc_end_io;
xfs_zone_gc_add_data(chunk);
data->scratch_head = (data->scratch_head + len) % data->scratch_size;
data->scratch_available -= len;
WRITE_ONCE(chunk->state, XFS_GC_BIO_NEW);
list_add_tail(&chunk->entry, &data->reading);
@ -862,6 +854,7 @@ xfs_zone_gc_finish_chunk(
data->scratch_tail =
(data->scratch_tail + chunk->len) % data->scratch_size;
data->scratch_available += chunk->len;
/*
* Cycle through the iolock and wait for direct I/O and layouts to