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Wire O_DIRECT also to Uncached I/O (#17218)

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Before Direct I/O was implemented, I've implemented lighter version
I called Uncached I/O.  It uses normal DMU/ARC data path with some
optimizations, but evicts data from caches as soon as possible and
reasonable.  Originally I wired it only to a primarycache property,
but now completing the integration all the way up to the VFS.

While Direct I/O has the lowest possible memory bandwidth usage,
it also has a significant number of limitations.  It require I/Os
to be page aligned, does not allow speculative prefetch, etc.  The
Uncached I/O does not have those limitations, but instead require
additional memory copy, though still one less than regular cached
I/O.  As such it should fill the gap in between.  Considering this
I've disabled annoying EINVAL errors on misaligned requests, adding
a tunable for those who wants to test their applications.

To pass the information between the layers I had to change a number
of APIs.  But as side effect upper layers can now control not only
the caching, but also speculative prefetch.  I haven't wired it to
VFS yet, since it require looking on some OS specifics.  But while
there I've implemented speculative prefetch of indirect blocks for
Direct I/O, controllable via all the same mechanisms.

Signed-off-by:	Alexander Motin <mav@FreeBSD.org>
Sponsored by:	iXsystems, Inc.
Fixes #17027
Reviewed-by: Rob Norris <robn@despairlabs.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
This commit is contained in:
Alexander Motin
2025-05-13 17:26:55 -04:00
committed by GitHub
parent e2ba0f7643
commit 734eba251d
35 changed files with 397 additions and 294 deletions
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module/zfs/dnode.c
+2 -2
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@@ -1510,7 +1510,7 @@ dnode_hold_impl(objset_t *os, uint64_t object, int flag, int slots,
* if we get the encrypted or decrypted version.
*/
err = dbuf_read(db, NULL, DB_RF_CANFAIL |
DB_RF_NO_DECRYPT | DB_RF_NOPREFETCH);
DMU_READ_NO_PREFETCH | DMU_READ_NO_DECRYPT);
if (err) {
DNODE_STAT_BUMP(dnode_hold_dbuf_read);
dbuf_rele(db, FTAG);
@@ -2578,7 +2578,7 @@ dnode_next_offset_level(dnode_t *dn, int flags, uint64_t *offset,
}
error = dbuf_read(db, NULL,
DB_RF_CANFAIL | DB_RF_HAVESTRUCT |
DB_RF_NO_DECRYPT | DB_RF_NOPREFETCH);
DMU_READ_NO_PREFETCH | DMU_READ_NO_DECRYPT);
if (error) {
dbuf_rele(db, FTAG);
return (error);