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a10e552b99
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 request 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
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 controls 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.
ZVOLs and dedup is not currently supported with Direct I/O.
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 parameter zfs_dio_enabled that can be used to
force all reads and writes through the ARC. By setting this module
parameter to 0, it mimics as if the direct dataset property is set to
disabled.
Reviewed-by: Brian Behlendorf <behlendorf@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Tony Hutter <hutter2@llnl.gov>
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>
Closes #10018
276 lines
6.8 KiB
Plaintext
276 lines
6.8 KiB
Plaintext
dnl #
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dnl # Check for available iov_iter functionality.
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dnl #
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AC_DEFUN([ZFS_AC_KERNEL_SRC_VFS_IOV_ITER], [
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ZFS_LINUX_TEST_SRC([iov_iter_types], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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int type __attribute__ ((unused)) = ITER_KVEC;
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])
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ZFS_LINUX_TEST_SRC([iov_iter_advance], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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size_t advance = 512;
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iov_iter_advance(&iter, advance);
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])
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ZFS_LINUX_TEST_SRC([iov_iter_revert], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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size_t revert = 512;
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iov_iter_revert(&iter, revert);
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])
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ZFS_LINUX_TEST_SRC([iov_iter_fault_in_readable], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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size_t size = 512;
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int error __attribute__ ((unused));
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error = iov_iter_fault_in_readable(&iter, size);
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])
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ZFS_LINUX_TEST_SRC([fault_in_iov_iter_readable], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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size_t size = 512;
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int error __attribute__ ((unused));
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error = fault_in_iov_iter_readable(&iter, size);
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])
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ZFS_LINUX_TEST_SRC([iov_iter_count], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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size_t bytes __attribute__ ((unused));
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bytes = iov_iter_count(&iter);
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])
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ZFS_LINUX_TEST_SRC([copy_to_iter], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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char buf[512] = { 0 };
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size_t size = 512;
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size_t bytes __attribute__ ((unused));
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bytes = copy_to_iter((const void *)&buf, size, &iter);
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])
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ZFS_LINUX_TEST_SRC([copy_from_iter], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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char buf[512] = { 0 };
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size_t size = 512;
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size_t bytes __attribute__ ((unused));
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bytes = copy_from_iter((void *)&buf, size, &iter);
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])
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ZFS_LINUX_TEST_SRC([iov_iter_get_pages2], [
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#include <linux/uio.h>
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], [
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struct iov_iter iter = { 0 };
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struct page **pages = NULL;
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size_t maxsize = 4096;
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unsigned maxpages = 1;
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size_t start;
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size_t ret __attribute__ ((unused));
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ret = iov_iter_get_pages2(&iter, pages, maxsize, maxpages,
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&start);
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])
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ZFS_LINUX_TEST_SRC([iov_iter_get_pages], [
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#include <linux/uio.h>
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], [
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struct iov_iter iter = { 0 };
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struct page **pages = NULL;
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size_t maxsize = 4096;
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unsigned maxpages = 1;
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size_t start;
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size_t ret __attribute__ ((unused));
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ret = iov_iter_get_pages(&iter, pages, maxsize, maxpages,
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&start);
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])
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ZFS_LINUX_TEST_SRC([iov_iter_type], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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__attribute__((unused)) enum iter_type i = iov_iter_type(&iter);
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])
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ZFS_LINUX_TEST_SRC([iter_iov], [
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#include <linux/fs.h>
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#include <linux/uio.h>
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],[
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struct iov_iter iter = { 0 };
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__attribute__((unused)) const struct iovec *iov = iter_iov(&iter);
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])
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])
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AC_DEFUN([ZFS_AC_KERNEL_VFS_IOV_ITER], [
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enable_vfs_iov_iter="yes"
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AC_MSG_CHECKING([whether iov_iter types are available])
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ZFS_LINUX_TEST_RESULT([iov_iter_types], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_IOV_ITER_TYPES, 1,
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[iov_iter types are available])
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],[
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AC_MSG_RESULT(no)
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enable_vfs_iov_iter="no"
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])
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AC_MSG_CHECKING([whether iov_iter_advance() is available])
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ZFS_LINUX_TEST_RESULT([iov_iter_advance], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_IOV_ITER_ADVANCE, 1,
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[iov_iter_advance() is available])
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],[
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AC_MSG_RESULT(no)
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enable_vfs_iov_iter="no"
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])
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AC_MSG_CHECKING([whether iov_iter_revert() is available])
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ZFS_LINUX_TEST_RESULT([iov_iter_revert], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_IOV_ITER_REVERT, 1,
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[iov_iter_revert() is available])
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],[
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AC_MSG_RESULT(no)
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enable_vfs_iov_iter="no"
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])
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AC_MSG_CHECKING([whether iov_iter_fault_in_readable() is available])
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ZFS_LINUX_TEST_RESULT([iov_iter_fault_in_readable], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_IOV_ITER_FAULT_IN_READABLE, 1,
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[iov_iter_fault_in_readable() is available])
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],[
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AC_MSG_RESULT(no)
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AC_MSG_CHECKING([whether fault_in_iov_iter_readable() is available])
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ZFS_LINUX_TEST_RESULT([fault_in_iov_iter_readable], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_FAULT_IN_IOV_ITER_READABLE, 1,
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[fault_in_iov_iter_readable() is available])
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],[
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AC_MSG_RESULT(no)
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enable_vfs_iov_iter="no"
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])
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])
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AC_MSG_CHECKING([whether iov_iter_count() is available])
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ZFS_LINUX_TEST_RESULT([iov_iter_count], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_IOV_ITER_COUNT, 1,
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[iov_iter_count() is available])
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],[
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AC_MSG_RESULT(no)
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enable_vfs_iov_iter="no"
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])
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AC_MSG_CHECKING([whether copy_to_iter() is available])
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ZFS_LINUX_TEST_RESULT([copy_to_iter], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_COPY_TO_ITER, 1,
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[copy_to_iter() is available])
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],[
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AC_MSG_RESULT(no)
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enable_vfs_iov_iter="no"
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])
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AC_MSG_CHECKING([whether copy_from_iter() is available])
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ZFS_LINUX_TEST_RESULT([copy_from_iter], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_COPY_FROM_ITER, 1,
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[copy_from_iter() is available])
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],[
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AC_MSG_RESULT(no)
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enable_vfs_iov_iter="no"
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])
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dnl #
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dnl # Kernel 6.0 changed iov_iter_get_pages() to iov_iter_page_pages2().
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dnl #
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AC_MSG_CHECKING([whether iov_iter_get_pages2() is available])
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ZFS_LINUX_TEST_RESULT([iov_iter_get_pages2], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_IOV_ITER_GET_PAGES2, 1,
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[iov_iter_get_pages2() is available])
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], [
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AC_MSG_RESULT(no)
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AC_MSG_CHECKING([whether iov_iter_get_pages() is available])
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ZFS_LINUX_TEST_RESULT([iov_iter_get_pages], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_IOV_ITER_GET_PAGES, 1,
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[iov_iter_get_pages() is available])
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], [
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AC_MSG_RESULT(no)
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enable_vfs_iov_iter="no"
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])
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])
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dnl #
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dnl # This checks for iov_iter_type() in linux/uio.h. It is not
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dnl # required, however, and the module will compiled without it
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dnl # using direct access of the member attribute
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dnl #
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AC_MSG_CHECKING([whether iov_iter_type() is available])
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ZFS_LINUX_TEST_RESULT([iov_iter_type], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_IOV_ITER_TYPE, 1,
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[iov_iter_type() is available])
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],[
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AC_MSG_RESULT(no)
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])
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dnl #
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dnl # As of the 4.9 kernel support is provided for iovecs, kvecs,
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dnl # bvecs and pipes in the iov_iter structure. As long as the
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dnl # other support interfaces are all available the iov_iter can
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dnl # be correctly used in the uio structure.
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dnl #
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AS_IF([test "x$enable_vfs_iov_iter" = "xyes"], [
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AC_DEFINE(HAVE_VFS_IOV_ITER, 1,
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[All required iov_iter interfaces are available])
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])
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dnl #
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dnl # Kernel 6.5 introduces the iter_iov() function that returns the
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dnl # __iov member of an iov_iter*. The iov member was renamed to this
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dnl # __iov member, and is intended to be accessed via the helper
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dnl # function now.
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dnl #
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AC_MSG_CHECKING([whether iter_iov() is available])
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ZFS_LINUX_TEST_RESULT([iter_iov], [
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AC_MSG_RESULT(yes)
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AC_DEFINE(HAVE_ITER_IOV, 1,
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[iter_iov() is available])
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],[
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AC_MSG_RESULT(no)
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])
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])
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