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DDT: Add/use zap_lookup_length_uint64_by_dnode()

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Unlike other ZAP consumers due to compression DDT does not know
how big entry it is reading from ZAP.  Due to this it called
zap_length_uint64_by_dnode() and zap_lookup_uint64_by_dnode(),
each of which does full ZAP entry lookup.

Introduction of the combined ZAP method dramatically reduces the
CPU overhead and locks contention at DBUF layer.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Alexander Motin <alexander.motin@TrueNAS.com>
Closes #18048
This commit is contained in:
Alexander Motin
2025-12-15 17:38:34 -05:00
committed by Tony Hutter
parent 4905686e67
commit 4ab2027f59
5 changed files with 46 additions and 26 deletions
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module/zfs/ddt_zap.c
+8 -14
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@@ -124,25 +124,19 @@ static int
ddt_zap_lookup(dnode_t *dn, const ddt_key_t *ddk, void *phys, size_t psize)
{
uchar_t *cbuf;
uint64_t one, csize;
uint64_t csize;
int error;
error = zap_length_uint64_by_dnode(dn, (uint64_t *)ddk,
DDT_KEY_WORDS, &one, &csize);
if (error)
return (error);
cbuf = kmem_alloc(psize + 1, KM_SLEEP);
ASSERT3U(one, ==, 1);
ASSERT3U(csize, <=, psize + 1);
cbuf = kmem_alloc(csize, KM_SLEEP);
error = zap_lookup_uint64_by_dnode(dn, (uint64_t *)ddk,
DDT_KEY_WORDS, 1, csize, cbuf);
if (error == 0)
error = zap_lookup_length_uint64_by_dnode(dn, (uint64_t *)ddk,
DDT_KEY_WORDS, 1, psize + 1, cbuf, &csize);
if (error == 0) {
ASSERT3U(csize, <=, psize + 1);
ddt_zap_decompress(cbuf, phys, csize, psize);
}
kmem_free(cbuf, csize);
kmem_free(cbuf, psize + 1);
return (error);
}