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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/dmu_zfetch.c
+5 -4
View File
@@ -690,7 +690,7 @@ prescient:
void
dmu_zfetch_run(zfetch_t *zf, zstream_t *zs, boolean_t missed,
boolean_t have_lock)
boolean_t have_lock, boolean_t uncached)
{
int64_t pf_start, pf_end, ipf_start, ipf_end;
int epbs, issued;
@@ -745,7 +745,8 @@ dmu_zfetch_run(zfetch_t *zf, zstream_t *zs, boolean_t missed,
issued = 0;
for (int64_t blk = pf_start; blk < pf_end; blk++) {
issued += dbuf_prefetch_impl(zf->zf_dnode, 0, blk,
ZIO_PRIORITY_ASYNC_READ, 0, dmu_zfetch_done, zs);
ZIO_PRIORITY_ASYNC_READ, uncached ?
ARC_FLAG_UNCACHED : 0, dmu_zfetch_done, zs);
}
for (int64_t iblk = ipf_start; iblk < ipf_end; iblk++) {
issued += dbuf_prefetch_impl(zf->zf_dnode, 1, iblk,
@@ -761,13 +762,13 @@ dmu_zfetch_run(zfetch_t *zf, zstream_t *zs, boolean_t missed,
void
dmu_zfetch(zfetch_t *zf, uint64_t blkid, uint64_t nblks, boolean_t fetch_data,
boolean_t missed, boolean_t have_lock)
boolean_t missed, boolean_t have_lock, boolean_t uncached)
{
zstream_t *zs;
zs = dmu_zfetch_prepare(zf, blkid, nblks, fetch_data, have_lock);
if (zs)
dmu_zfetch_run(zf, zs, missed, have_lock);
dmu_zfetch_run(zf, zs, missed, have_lock, uncached);
}
ZFS_MODULE_PARAM(zfs_prefetch, zfs_prefetch_, disable, INT, ZMOD_RW,