c/mirror_zfs
1
0
Fork 0
mirror of https://git.proxmox.com/git/mirror_zfs.git synced 2026-05-25 11:47:43 +03:00
Code Issues Packages Projects Releases Wiki Activity

Improve caching for dbuf prefetches

Browse Source 
To avoid read errors with transaction open dmu_tx_check_ioerr()
is used to read everything required in advance.  But there seems
to be a chance for the buffer to evicted from dbuf cache in
between, which result in immediate eviction from ARC, which may
require additional disk read later in a place where error handling
is problematic.

To partially workaround this introduce a new flag DMU_IS_PREFETCH,
relayed to ARC as ARC_FLAG_PREFETCH | ARC_FLAG_PRESCIENT_PREFETCH,
making ARC delay eviction by at least several seconds, or till the
actual read inside the transaction, that will promote it to demand
access.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Signed-off-by: Alexander Motin <alexander.motin@TrueNAS.com>
Closes #18160
This commit is contained in:
Alexander Motin
2026-02-04 13:12:32 -05:00
committed by Tony Hutter
parent 11647c669e
commit 25327ed7ce
3 changed files with 8 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files
module/zfs/dmu_tx.c
+4 -3
View File
@@ -220,11 +220,12 @@ dmu_tx_check_ioerr(zio_t *zio, dnode_t *dn, int level, uint64_t blkid)
if (err != 0)
return (err);
/*
* PARTIAL_FIRST allows caching for uncacheable blocks. It will
* be cleared after dmu_buf_will_dirty() call dbuf_read() again.
* DMU_IS_PREFETCH keeps the buffer temporarily in DBUF cache and ARC
* to avoid immediate eviction after the check. It will be promoted
* to demand access when dmu_buf_will_dirty() read it again.
*/
err = dbuf_read(db, zio, DB_RF_CANFAIL | DMU_READ_NO_PREFETCH |
(level == 0 ? (DMU_UNCACHEDIO | DMU_PARTIAL_FIRST) : 0));
(level == 0 ? (DMU_KEEP_CACHING | DMU_IS_PREFETCH) : 0));
dbuf_rele(db, FTAG);
return (err);
}