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ZIL: Make allocations more flexible

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When ZIL allocates space for new LWBs without knowing how much it
will require, it can use new metaslab_alloc_range() function to
allocate slightly more or less than it predicted.  It allows to
improve space efficiency by allocating bigger LWBs on RAIDZ/dRAID
instead of padding and possibly packing more ZIL records there.
It may also allow to reduce ganging in some cases by allowing to
allocate smaller LWBs when we are not sure we'll need bigger.

On the opposite side, when we allocate space for already closed
LWBs, when we precisely know how much space we need, we may just
allocate what we need instead of relying on writing less than
allocated, that does not work for RAIDZ.

Space for LWBs in open state (still being filled) is allocated
same as before.

Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <alexander.motin@TrueNAS.com>
Closes #17613
This commit is contained in:
Alexander Motin
2025-08-14 11:50:17 -04:00
committed by GitHub
parent 8d35a022e4
commit d151432073
4 changed files with 180 additions and 105 deletions
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include/sys/zio.h
+2 -1
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@@ -622,7 +622,8 @@ extern zio_t *zio_free_sync(zio_t *pio, spa_t *spa, uint64_t txg,
const blkptr_t *bp, zio_flag_t flags);
extern int zio_alloc_zil(spa_t *spa, objset_t *os, uint64_t txg,
blkptr_t *new_bp, uint64_t size, boolean_t *slog);
blkptr_t *new_bp, uint64_t min_size, uint64_t max_size, boolean_t *slog,
boolean_t allow_larger);
extern void zio_flush(zio_t *zio, vdev_t *vd);
extern void zio_shrink(zio_t *zio, uint64_t size);