Linux 5.15 compat: block device readahead

The 5.15 kernel moved the backing_dev_info structure out of
the request queue structure which causes a build failure.

Rather than look in the new location for the BDI we instead
detect this upstream refactoring by the existance of either
the blk_queue_update_readahead() or disk_update_readahead()
functions.  In either case, there's no longer any reason to
manually set the ra_pages value since it will be overridden
with a reasonable default (2x the block size) when
blk_queue_io_opt() is called.

Therefore, we update the compatibility wrapper to do nothing
for 5.9 and newer kernels.  While it's tempting to do the
same for older kernels we want to keep the compatibility
code to preserve the existing behavior.  Removing it would
effectively increase the default readahead to 128k.

Reviewed-by: Tony Nguyen <tony.nguyen@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #12532

diff --git a/config/kernel-blk-queue.m4 b/config/kernel-blk-queue.m4
index 1dced82ce6863a71dfa79725170088e90b66bb6d..ff5d2d370e98a0e1bafe86c383f2b6fe6924c04c 100644 (file)
--- a/config/kernel-blk-queue.m4
+++ b/config/kernel-blk-queue.m4
@@ -47,6 +47,44 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE_BDI], [
        ])
 ])
 
+dnl #
+dnl # 5.9: added blk_queue_update_readahead(),
+dnl # 5.15: renamed to disk_update_readahead()
+dnl #
+AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_QUEUE_UPDATE_READAHEAD], [
+       ZFS_LINUX_TEST_SRC([blk_queue_update_readahead], [
+               #include <linux/blkdev.h>
+       ],[
+               struct request_queue q;
+               blk_queue_update_readahead(&q);
+       ])
+
+       ZFS_LINUX_TEST_SRC([disk_update_readahead], [
+               #include <linux/blkdev.h>
+       ],[
+               struct gendisk disk;
+               disk_update_readahead(&disk);
+       ])
+])
+
+AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE_UPDATE_READAHEAD], [
+       AC_MSG_CHECKING([whether blk_queue_update_readahead() exists])
+       ZFS_LINUX_TEST_RESULT([blk_queue_update_readahead], [
+               AC_MSG_RESULT(yes)
+               AC_DEFINE(HAVE_BLK_QUEUE_UPDATE_READAHEAD, 1,
+                   [blk_queue_update_readahead() exists])
+       ],[
+               AC_MSG_CHECKING([whether disk_update_readahead() exists])
+               ZFS_LINUX_TEST_RESULT([disk_update_readahead], [
+                       AC_MSG_RESULT(yes)
+                       AC_DEFINE(HAVE_DISK_UPDATE_READAHEAD, 1,
+                           [disk_update_readahead() exists])
+               ],[
+                       AC_MSG_RESULT(no)
+               ])
+       ])
+])
+
 dnl #
 dnl # 2.6.32 API,
 dnl #   blk_queue_discard()
@@ -280,6 +318,7 @@ AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE_MAX_SEGMENTS], [
 AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_QUEUE], [
        ZFS_AC_KERNEL_SRC_BLK_QUEUE_PLUG
        ZFS_AC_KERNEL_SRC_BLK_QUEUE_BDI
+       ZFS_AC_KERNEL_SRC_BLK_QUEUE_UPDATE_READAHEAD
        ZFS_AC_KERNEL_SRC_BLK_QUEUE_DISCARD
        ZFS_AC_KERNEL_SRC_BLK_QUEUE_SECURE_ERASE
        ZFS_AC_KERNEL_SRC_BLK_QUEUE_FLAG_SET
@@ -292,6 +331,7 @@ AC_DEFUN([ZFS_AC_KERNEL_SRC_BLK_QUEUE], [
 AC_DEFUN([ZFS_AC_KERNEL_BLK_QUEUE], [
        ZFS_AC_KERNEL_BLK_QUEUE_PLUG
        ZFS_AC_KERNEL_BLK_QUEUE_BDI
+       ZFS_AC_KERNEL_BLK_QUEUE_UPDATE_READAHEAD
        ZFS_AC_KERNEL_BLK_QUEUE_DISCARD
        ZFS_AC_KERNEL_BLK_QUEUE_SECURE_ERASE
        ZFS_AC_KERNEL_BLK_QUEUE_FLAG_SET

diff --git a/include/os/linux/kernel/linux/blkdev_compat.h b/include/os/linux/kernel/linux/blkdev_compat.h
index 87d541072015a12446465745cf138c443dc67242..019d5390adec74621d5c2151d2cc410bf9c0cd83 100644 (file)
--- a/include/os/linux/kernel/linux/blkdev_compat.h
+++ b/include/os/linux/kernel/linux/blkdev_compat.h
@@ -92,11 +92,14 @@ blk_queue_set_write_cache(struct request_queue *q, bool wc, bool fua)
 static inline void
 blk_queue_set_read_ahead(struct request_queue *q, unsigned long ra_pages)
 {
+#if !defined(HAVE_BLK_QUEUE_UPDATE_READAHEAD) && \
+       !defined(HAVE_DISK_UPDATE_READAHEAD)
 #ifdef HAVE_BLK_QUEUE_BDI_DYNAMIC
        q->backing_dev_info->ra_pages = ra_pages;
 #else
        q->backing_dev_info.ra_pages = ra_pages;
 #endif
+#endif
 }
 
 #ifdef HAVE_BIO_BVEC_ITER