Updating code based on PR code comments. I adjusted the following parts
of code based on comments:
1. Revert dbuf_undirty() to original logic and got rid of uncessary
code change.
2. Cleanup in abd_impl.h
3. Cleanup in abd.h
4. Got rid of duplicate declaration of dmu_buf_hold_noread() in dmu.h.
5. Cleaned up comment for db_mtx in dmu_imp.h
6. Updated zfsprop man page to state correct ZFS version
7. Updated to correct cast in zfs_uio_page_aligned() calls to use
uintptr_t.
8. Cleaned up comment in FreeBSD uio code.
9. Removed unnecessary format changes in comments in Linux abd code.
10. Updated ZFS VFS hook for direct_IO to use PANIC().
11. Updated comment above dbuf_undirty to use double space again.
12. Converted module paramter zfs_vdev_direct_write_verify_pct OS
indedepent and in doing so this removed the uneccessary check for
bounds.
13. Updated to casting in zfs_dio_page_aligned to uniptr_t and added
kernel guard.
14. Updated zfs_dio_size_aligned() to use modulo math because
dn->dn_datablksz is not required to be a power of 2.
15. Removed abd scatter stats update calls from all
ABD_FLAG_FROM_PAGES.
16. Updated check in abd_alloc_from_pages() for the linear page. This
way a single page that is even 4K can represented as an
ABD_FLAG_LINEAR_PAGE.
17. Fixing types for UIO code. In FreeBSD the vm code expects and
returns int's for values. In linux the interfaces return long value
in get_user_pages_unlocked() and rest of the IOV interfaces return
int's. Stuck with the worse case and used long for npages in Linux.
Updated the uio npage struct to correspond to the correct types and
that type checking is consistent in the UIO code.
18. Updated comments about what zfs_uio_get_pages_alloc() is doing.
19. Updated error handeling in zfs_uio_get_dio_pages_alloc() for Linux.
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Adding O_DIRECT support to ZFS to bypass the ARC for writes/reads.
O_DIRECT support in ZFS will always ensure there is coherency between
buffered and O_DIRECT IO requests. This ensures that all IO requests,
whether buffered or direct, will see the same file contents at all
times. Just as in other FS's , O_DIRECT does not imply O_SYNC. While
data is written directly to VDEV disks, metadata will not be synced
until the associated TXG is synced.
For both O_DIRECT read and write request the offset and requeset sizes,
at a minimum, must be PAGE_SIZE aligned. In the event they are not,
then EINVAL is returned unless the direct property is set to always (see
below).
For O_DIRECT writes:
The request also must be block aligned (recordsize) or the write
request will take the normal (buffered) write path. In the event that
request is block aligned and a cached copy of the buffer in the ARC,
then it will be discarded from the ARC forcing all further reads to
retrieve the data from disk.
For O_DIRECT reads:
The only alignment restrictions are PAGE_SIZE alignment. In the event
that the requested data is in buffered (in the ARC) it will just be
copied from the ARC into the user buffer.
For both O_DIRECT writes and reads the O_DIRECT flag will be ignored in
the event that file contents are mmap'ed. In this case, all requests
that are at least PAGE_SIZE aligned will just fall back to the buffered
paths. If the request however is not PAGE_SIZE aligned, EINVAL will
be returned as always regardless if the file's contents are mmap'ed.
Since O_DIRECT writes go through the normal ZIO pipeline, the
following operations are supported just as with normal buffered writes:
Checksum
Compression
Dedup
Encryption
Erasure Coding
There is one caveat for the data integrity of O_DIRECT writes that is
distinct for each of the OS's supported by ZFS.
FreeBSD - FreeBSD is able to place user pages under write protection so
any data in the user buffers and written directly down to the
VDEV disks is guaranteed to not change. There is no concern
with data integrity and O_DIRECT writes.
Linux - Linux is not able to place anonymous user pages under write
protection. Because of this, if the user decides to manipulate
the page contents while the write operation is occurring, data
integrity can not be guaranteed. However, there is a module
parameter `zfs_vdev_direct_write_verify` that contols the
if a O_DIRECT writes that can occur to a top-level VDEV before
a checksum verify is run before the contents of the I/O buffer
are committed to disk. In the event of a checksum verification
failure the write will return EIO. The number of O_DIRECT write
checksum verification errors can be observed by doing
`zpool status -d`, which will list all verification errors that
have occurred on a top-level VDEV. Along with `zpool status`, a
ZED event will be issues as `dio_verify` when a checksum
verification error occurs.
A new dataset property `direct` has been added with the following 3
allowable values:
disabled - Accepts O_DIRECT flag, but silently ignores it and treats
the request as a buffered IO request.
standard - Follows the alignment restrictions outlined above for
write/read IO requests when the O_DIRECT flag is used.
always - Treats every write/read IO request as though it passed
O_DIRECT and will do O_DIRECT if the alignment restrictions
are met otherwise will redirect through the ARC. This
property will not allow a request to fail.
There is also a module paramter zfs_dio_enabled that can be used to
force all reads and writes through the ARC. By setting this module
paramter to 0, it mimics as if the direct dataset property is set to
disabled.
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Co-authored-by: Mark Maybee <mark.maybee@delphix.com>
Co-authored-by: Matt Macy <mmacy@FreeBSD.org>
Co-authored-by: Brian Behlendorf <behlendorf@llnl.gov>
Making uio_impl.h the common header interface between Linux and FreeBSD
so both OS's can share a common header file. This also helps reduce code
duplication for zfs_uio_t for each OS.
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Closes#11622
In FreeBSD the struct uio was just a typedef to uio_t. In order to
extend this struct, outside of the definition for the struct uio, the
struct uio has been embedded inside of a uio_t struct.
Also renamed all the uio_* interfaces to be zfs_uio_* to make it clear
this is a ZFS interface.
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Jorgen Lundman <lundman@lundman.net>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Brian Atkinson <batkinson@lanl.gov>
Closes#11438
The bug time sequence:
1. thread #1, `zfs_write` assign a txg "n".
2. In a same process, thread #2, mmap page fault (which means the
`mm_sem` is hold) occurred, `zfs_dirty_inode` open a txg failed,
and wait previous txg "n" completed.
3. thread #1 call `uiomove` to write, however page fault is occurred
in `uiomove`, which means it need `mm_sem`, but `mm_sem` is hold by
thread #2, so it stuck and can't complete, then txg "n" will
not complete.
So thread #1 and thread #2 are deadlocked.
Reviewed-by: Chunwei Chen <tuxoko@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Signed-off-by: Grady Wong <grady.w@xtaotech.com>
Closes#7939
This code originates in OpenSolaris and was modified by KQ Infotech
to be compatible with Linux. While supporting uios in the short
term is useful to get something working this is not an abstraction
we want to keep. This code is expected to be short lived and
removed as soon as all the remaining uio based APIs and updated.
Brian Atkinson
Tino Reichardt
ilbsmart
Brian Behlendorf