From ba6d0fb06039a75cbadef4a08cd42a259c54b8ef Mon Sep 17 00:00:00 2001 From: Rob Norris Date: Tue, 9 Jan 2024 13:28:57 +1100 Subject: [PATCH] vdev_disk: add module parameter to select BIO submission method This makes the submission method selectable at module load time via the `zfs_vdev_disk_classic` parameter, allowing this change to be backported to 2.2 safely, and disabled in favour of the "classic" submission method if new problems come up. Signed-off-by: Rob Norris Sponsored-by: Klara, Inc. Sponsored-by: Wasabi Technology, Inc. (cherry picked from commit 2382fdb0a83a5a3c6cf3860695d3f29281773170) --- man/man4/zfs.4 | 16 ++++++++++++++++ module/os/linux/zfs/vdev_disk.c | 31 +++++++++++++++++++++++++++++-- 2 files changed, 45 insertions(+), 2 deletions(-) diff --git a/man/man4/zfs.4 b/man/man4/zfs.4 index d840ae9a16..55580c9376 100644 --- a/man/man4/zfs.4 +++ b/man/man4/zfs.4 @@ -1312,6 +1312,22 @@ If this is higher than the maximum allowed by the device queue or the kernel itself, it will be clamped. Setting it to zero will cause the kernel's ideal size to be used. This parameter only applies on Linux. +This parameter is ignored if +.Sy zfs_vdev_disk_classic Ns = Ns Sy 1 . +. +.It Sy zfs_vdev_disk_classic Ns = Ns Sy 0 Ns | Ns 1 Pq uint +If set to 1, OpenZFS will submit IO to Linux using the method it used in 2.2 +and earlier. +This "classic" method has known issues with highly fragmented IO requests and +is slower on many workloads, but it has been in use for many years and is known +to be very stable. +If you set this parameter, please also open a bug report why you did so, +including the workload involved and any error messages. +.Pp +This parameter and the classic submission method will be removed once we have +total confidence in the new method. +.Pp +This parameter only applies on Linux, and can only be set at module load time. . .It Sy zfs_expire_snapshot Ns = Ns Sy 300 Ns s Pq int Time before expiring diff --git a/module/os/linux/zfs/vdev_disk.c b/module/os/linux/zfs/vdev_disk.c index 5902904918..808b561b99 100644 --- a/module/os/linux/zfs/vdev_disk.c +++ b/module/os/linux/zfs/vdev_disk.c @@ -1412,6 +1412,29 @@ vdev_disk_rele(vdev_t *vd) /* XXX: Implement me as a vnode rele for the device */ } +/* + * BIO submission method. See comment above about vdev_classic. + * Set zfs_vdev_disk_classic=0 for new, =1 for classic + */ +static uint_t zfs_vdev_disk_classic = 0; /* default new */ + +/* Set submission function from module parameter */ +static int +vdev_disk_param_set_classic(const char *buf, zfs_kernel_param_t *kp) +{ + int err = param_set_uint(buf, kp); + if (err < 0) + return (SET_ERROR(err)); + + vdev_disk_io_rw_fn = + zfs_vdev_disk_classic ? vdev_classic_physio : vdev_disk_io_rw; + + printk(KERN_INFO "ZFS: forcing %s BIO submission\n", + zfs_vdev_disk_classic ? "classic" : "new"); + + return (0); +} + /* * At first use vdev use, set the submission function from the default value if * it hasn't been set already. @@ -1424,8 +1447,8 @@ vdev_disk_init(spa_t *spa, nvlist_t *nv, void **tsd) (void) tsd; if (vdev_disk_io_rw_fn == NULL) - /* XXX make configurable */ - vdev_disk_io_rw_fn = 0 ? vdev_classic_physio : vdev_disk_io_rw; + vdev_disk_io_rw_fn = zfs_vdev_disk_classic ? + vdev_classic_physio : vdev_disk_io_rw; return (0); } @@ -1526,3 +1549,7 @@ ZFS_MODULE_PARAM(zfs_vdev, zfs_vdev_, open_timeout_ms, UINT, ZMOD_RW, ZFS_MODULE_PARAM(zfs_vdev_disk, zfs_vdev_disk_, max_segs, UINT, ZMOD_RW, "Maximum number of data segments to add to an IO request (min 4)"); + +ZFS_MODULE_PARAM_CALL(zfs_vdev_disk, zfs_vdev_disk_, classic, + vdev_disk_param_set_classic, param_get_uint, ZMOD_RD, + "Use classic BIO submission method");