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mirror_zfs/config/kernel-bdi.m4

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Add backing_device_info per-filesystem For a long time now the kernel has been moving away from using the pdflush daemon to write 'old' dirty pages to disk. The primary reason for this is because the pdflush daemon is single threaded and can be a limiting factor for performance. Since pdflush sequentially walks the dirty inode list for each super block any delay in processing can slow down dirty page writeback for all filesystems. The replacement for pdflush is called bdi (backing device info). The bdi system involves creating a per-filesystem control structure each with its own private sets of queues to manage writeback. The advantage is greater parallelism which improves performance and prevents a single filesystem from slowing writeback to the others. For a long time both systems co-existed in the kernel so it wasn't strictly required to implement the bdi scheme. However, as of Linux 2.6.36 kernels the pdflush functionality has been retired. Since ZFS already bypasses the page cache for most I/O this is only an issue for mmap(2) writes which must go through the page cache. Even then adding this missing support for newer kernels was overlooked because there are other mechanisms which can trigger writeback. However, there is one critical case where not implementing the bdi functionality can cause problems. If an application handles a page fault it can enter the balance_dirty_pages() callpath. This will result in the application hanging until the number of dirty pages in the system drops below the dirty ratio. Without a registered backing_device_info for the filesystem the dirty pages will not get written out. Thus the application will hang. As mentioned above this was less of an issue with older kernels because pdflush would eventually write out the dirty pages. This change adds a backing_device_info structure to the zfs_sb_t which is already allocated per-super block. It is then registered when the filesystem mounted and unregistered on unmount. It will not be registered for mounted snapshots which are read-only. This change will result in flush-<pool> thread being dynamically created and destroyed per-mounted filesystem for writeback. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #174
2011-08-02 05:24:40 +04:00
dnl #
dnl # 2.6.32 API change
dnl # Private backing_device_info interfaces available
dnl #
AC_DEFUN([ZFS_AC_KERNEL_BDI], [
AC_MSG_CHECKING([whether super_block has s_bdi])
ZFS_LINUX_TRY_COMPILE([
#include <linux/fs.h>
Stop runtime pointer modifications in autotools checks c38367c73f592ca9729ba0d5e70b5e3bc67e0745 was meant to eliminate runtime function pointer modifications in autotools checks because they were prone to false negatives on kernels hardened by the PaX project. Unfortunately, I missed the xattr_handler and super_block->s_bdi autotools checks. Recent changes to PaX constified xattr_handler->get/set, which lead me to discover this oversight. Signed-off-by: Richard Yao <ryao@gentoo.org> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1433
2013-09-10 23:13:44 +04:00
static const struct super_block
Fix typos in commit b83e3e48c9b183a80dd00eb6c7431a1cbc7d89c9 There's a missing semicolon and equals sign in the first hunk of this commit in config/kernel-bdi.m4. This results in the test always failing. The effects were noticed when rrdtool, a tool which modifies files by mmap() and msync(), would have data never get saved to disk in spite of the files working while the mounted filesystem remains mounted. Signed-off-by: DHE <git@dehacked.net> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Richard Yao <ryao@gentoo.org> Closes #1889
2013-11-20 04:00:43 +04:00
sb __attribute__ ((unused)) = {
Stop runtime pointer modifications in autotools checks c38367c73f592ca9729ba0d5e70b5e3bc67e0745 was meant to eliminate runtime function pointer modifications in autotools checks because they were prone to false negatives on kernels hardened by the PaX project. Unfortunately, I missed the xattr_handler and super_block->s_bdi autotools checks. Recent changes to PaX constified xattr_handler->get/set, which lead me to discover this oversight. Signed-off-by: Richard Yao <ryao@gentoo.org> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #1433
2013-09-10 23:13:44 +04:00
.s_bdi = NULL,
Fix typos in commit b83e3e48c9b183a80dd00eb6c7431a1cbc7d89c9 There's a missing semicolon and equals sign in the first hunk of this commit in config/kernel-bdi.m4. This results in the test always failing. The effects were noticed when rrdtool, a tool which modifies files by mmap() and msync(), would have data never get saved to disk in spite of the files working while the mounted filesystem remains mounted. Signed-off-by: DHE <git@dehacked.net> Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Richard Yao <ryao@gentoo.org> Closes #1889
2013-11-20 04:00:43 +04:00
};
Add backing_device_info per-filesystem For a long time now the kernel has been moving away from using the pdflush daemon to write 'old' dirty pages to disk. The primary reason for this is because the pdflush daemon is single threaded and can be a limiting factor for performance. Since pdflush sequentially walks the dirty inode list for each super block any delay in processing can slow down dirty page writeback for all filesystems. The replacement for pdflush is called bdi (backing device info). The bdi system involves creating a per-filesystem control structure each with its own private sets of queues to manage writeback. The advantage is greater parallelism which improves performance and prevents a single filesystem from slowing writeback to the others. For a long time both systems co-existed in the kernel so it wasn't strictly required to implement the bdi scheme. However, as of Linux 2.6.36 kernels the pdflush functionality has been retired. Since ZFS already bypasses the page cache for most I/O this is only an issue for mmap(2) writes which must go through the page cache. Even then adding this missing support for newer kernels was overlooked because there are other mechanisms which can trigger writeback. However, there is one critical case where not implementing the bdi functionality can cause problems. If an application handles a page fault it can enter the balance_dirty_pages() callpath. This will result in the application hanging until the number of dirty pages in the system drops below the dirty ratio. Without a registered backing_device_info for the filesystem the dirty pages will not get written out. Thus the application will hang. As mentioned above this was less of an issue with older kernels because pdflush would eventually write out the dirty pages. This change adds a backing_device_info structure to the zfs_sb_t which is already allocated per-super block. It is then registered when the filesystem mounted and unregistered on unmount. It will not be registered for mounted snapshots which are read-only. This change will result in flush-<pool> thread being dynamically created and destroyed per-mounted filesystem for writeback. Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov> Closes #174
2011-08-02 05:24:40 +04:00
],[
],[
AC_MSG_RESULT(yes)
AC_DEFINE(HAVE_BDI, 1, [struct super_block has s_bdi])
],[
AC_MSG_RESULT(no)
])
])
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