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Avoid small buffer copying on write 

It is wrong for arc_write_ready() to use zfs_abd_scatter_enabled to
decide whether to reallocate/copy the buffer, because the answer is
OS-specific and depends on the buffer size.  Instead of that use
abd_size_alloc_linear(), moved into public header.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Alexander Motin <mav@FreeBSD.org>
Closes #12425
This commit is contained in:
Alexander Motin 2021-07-27 19:05:47 -04:00 committed by Brian Behlendorf
parent 5b860ae1fb
commit 415882d228
6 changed files with 6 additions and 5 deletions
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1
include/sys/abd.h
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@ -91,6 +91,7 @@ abd_t *abd_alloc_linear(size_t, boolean_t);
abd_t *abd_alloc_gang(void); abd_t *abd_alloc_gang(void);
abd_t *abd_alloc_for_io(size_t, boolean_t); abd_t *abd_alloc_for_io(size_t, boolean_t);
abd_t *abd_alloc_sametype(abd_t *, size_t); abd_t *abd_alloc_sametype(abd_t *, size_t);
boolean_t abd_size_alloc_linear(size_t);
void abd_gang_add(abd_t *, abd_t *, boolean_t); void abd_gang_add(abd_t *, abd_t *, boolean_t);
void abd_free(abd_t *); void abd_free(abd_t *);
abd_t *abd_get_offset(abd_t *, size_t); abd_t *abd_get_offset(abd_t *, size_t);

1
include/sys/abd_impl.h
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@ -68,7 +68,6 @@ abd_t *abd_get_offset_scatter(abd_t *, abd_t *, size_t, size_t);
void abd_free_struct_impl(abd_t *); void abd_free_struct_impl(abd_t *);
void abd_alloc_chunks(abd_t *, size_t); void abd_alloc_chunks(abd_t *, size_t);
void abd_free_chunks(abd_t *); void abd_free_chunks(abd_t *);
boolean_t abd_size_alloc_linear(size_t);
void abd_update_scatter_stats(abd_t *, abd_stats_op_t); void abd_update_scatter_stats(abd_t *, abd_stats_op_t);
void abd_update_linear_stats(abd_t *, abd_stats_op_t); void abd_update_linear_stats(abd_t *, abd_stats_op_t);
void abd_verify_scatter(abd_t *); void abd_verify_scatter(abd_t *);

2
module/os/freebsd/zfs/abd_os.c
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@ -131,7 +131,7 @@ abd_scatter_chunkcnt(abd_t *abd)
boolean_t boolean_t
abd_size_alloc_linear(size_t size) abd_size_alloc_linear(size_t size)
{ {
return (size < zfs_abd_scatter_min_size ? B_TRUE : B_FALSE); return (!zfs_abd_scatter_enabled || size < zfs_abd_scatter_min_size);
} }
void void

2
module/os/linux/zfs/abd_os.c
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@ -638,7 +638,7 @@ abd_alloc_zero_scatter(void)
boolean_t boolean_t
abd_size_alloc_linear(size_t size) abd_size_alloc_linear(size_t size)
{ {
return (size < zfs_abd_scatter_min_size ? B_TRUE : B_FALSE); return (!zfs_abd_scatter_enabled || size < zfs_abd_scatter_min_size);
} }
void void

2
module/zfs/abd.c
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@ -181,7 +181,7 @@ abd_free_struct(abd_t *abd)
abd_t * abd_t *
abd_alloc(size_t size, boolean_t is_metadata) abd_alloc(size_t size, boolean_t is_metadata)
{ {
if (!zfs_abd_scatter_enabled || abd_size_alloc_linear(size)) if (abd_size_alloc_linear(size))
return (abd_alloc_linear(size, is_metadata)); return (abd_alloc_linear(size, is_metadata));
VERIFY3U(size, <=, SPA_MAXBLOCKSIZE); VERIFY3U(size, <=, SPA_MAXBLOCKSIZE);

3
module/zfs/arc.c
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@ -6917,7 +6917,8 @@ arc_write_ready(zio_t *zio)
arc_hdr_alloc_abd(hdr, ARC_HDR_DO_ADAPT | ARC_HDR_ALLOC_RDATA | arc_hdr_alloc_abd(hdr, ARC_HDR_DO_ADAPT | ARC_HDR_ALLOC_RDATA |
ARC_HDR_USE_RESERVE); ARC_HDR_USE_RESERVE);
abd_copy(hdr->b_crypt_hdr.b_rabd, zio->io_abd, psize); abd_copy(hdr->b_crypt_hdr.b_rabd, zio->io_abd, psize);
} else if (zfs_abd_scatter_enabled || !arc_can_share(hdr, buf)) { } else if (!abd_size_alloc_linear(arc_buf_size(buf)) ||
!arc_can_share(hdr, buf)) {
/* /*
* Ideally, we would always copy the io_abd into b_pabd, but the * Ideally, we would always copy the io_abd into b_pabd, but the
* user may have disabled compressed ARC, thus we must check the * user may have disabled compressed ARC, thus we must check the