FAILED: patch "[PATCH] dm: fix IO splitting" failed to apply to 5.9-stable tree
Subsystems (3)
[email protected]
maintainerThe patch below does not apply to the 5.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From 3ee16db390b42b8a21f2ad2ea2518f3469c6e532 Mon Sep 17 00:00:00 2001
From: Mike Snitzer <[email protected]>
Date: Mon, 30 Nov 2020 10:57:43 -0500
Subject: [PATCH] dm: fix IO splitting
Commit 882ec4e609c1 ("dm table: stack 'chunk_sectors' limit to account for target-specific splitting") caused a couple regressions:
1) Using lcm_not_zero() when stacking chunk_sectors was a bug because chunk_sectors must reflect the most limited of all devices in the IO stack.
2) DM targets that set max_io_len but that do _not_ provide an .iterate_devices method no longer had there IO split properly.
And commit 5091cdec56fa ("dm: change max_io_len() to use blk_max_size_offset()") also caused a regression where DM no longer supported varied (per target) IO splitting. The implication being the potential for severely reduced performance for IO stacks that use a DM target like dm-cache to hide performance limitations of a slower device (e.g. one that requires 4K IO splitting).
Coming full circle: Fix all these issues by discontinuing stacking chunk_sectors up using ti->max_io_len in dm_calculate_queue_limits(), add optional chunk_sectors override argument to blk_max_size_offset() and update DM's max_io_len() to pass ti->max_io_len to its blk_max_size_offset() call.
Passing in an optional chunk_sectors override to blk_max_size_offset() allows for code reuse of block's centralized calculation for max IO size based on provided offset and split boundary.
block/blk-merge.c +1 -1
@@ -144,7 +144,7 @@ static struct bio *blk_bio_write_same_split(struct request_queue *q,static inline unsigned get_max_io_size (struct request_queue *q,struct bio *bio) { -unsigned sectors =blk_max_size_offset (q, bio->bi_iter.bi_sector); +unsigned sectors =blk_max_size_offset (q, bio->bi_iter.bi_sector,0 );unsigned max_sectors = sectors;unsigned pbs =queue_physical_block_size (q) >>SECTOR_SHIFT ;unsigned lbs =queue_logical_block_size (q) >>SECTOR_SHIFT ;
drivers/md/dm-table.c +0 -5
@@ -18,7 +18,6 @@#include <linux/mutex.h> #include <linux/delay.h> #include <linux/atomic.h> -#include <linux/lcm.h> #include <linux/blk-mq.h> #include <linux/mount.h> #include <linux/dax.h>
@@ -1449,10 +1448,6 @@ int dm_calculate_queue_limits(struct dm_table *table, zone_sectors = ti_limits.chunk_sectors; } -/* Stack chunk_sectors if target-specific splitting is required */ -if (ti->max_io_len) - ti_limits.chunk_sectors =lcm_not_zero (ti->max_io_len, - ti_limits.chunk_sectors);/* Set I/O hints portion of queue limits */ if (ti->type->io_hints) ti->type->io_hints (ti, &ti_limits);
drivers/md/dm.c +11 -8
@@ -1039,15 +1039,18 @@ static sector_t max_io_len(struct dm_target *ti, sector_t sector)sector_t max_len;/* -* Does the target need to split even further? -* - q->limits.chunk_sectors reflects ti->max_io_len so -* blk_max_size_offset() provides required splitting. -* - blk_max_size_offset() also respects q->limits.max_sectors +* Does the target need to split IO even further? +* - varied (per target) IO splitting is a tenet of DM; this +* explains why stacked chunk_sectors based splitting via +* blk_max_size_offset() isn't possible here. So pass in +* ti->max_io_len to override stacked chunk_sectors. */ - max_len =blk_max_size_offset (ti->table->md->queue, - target_offset); -if (len > max_len) - len = max_len; +if (ti->max_io_len) { + max_len =blk_max_size_offset (ti->table->md->queue, + target_offset, ti->max_io_len); +if (len > max_len) + len = max_len; + }return len; }
include/linux/blkdev.h +6 -5
@@ -1073,11 +1073,12 @@ static inline unsigned int blk_queue_get_max_sectors(struct request_queue *q,* file system requests. */ static inline unsigned int blk_max_size_offset (struct request_queue *q, -sector_t offset) +sector_t offset, +unsigned int chunk_sectors) { -unsigned int chunk_sectors = q->limits.chunk_sectors; - -if (!chunk_sectors) +if (!chunk_sectors && q->limits.chunk_sectors) + chunk_sectors = q->limits.chunk_sectors; +else return q->limits.max_sectors;if (likely (is_power_of_2 (chunk_sectors)))
@@ -1101,7 +1102,7 @@ static inline unsigned int blk_rq_get_max_sectors(struct request *rq, req_op(rq) == REQ_OP_SECURE_ERASE)return blk_queue_get_max_sectors (q,req_op (rq)); -return min (blk_max_size_offset (q, offset), +return min (blk_max_size_offset (q, offset,0 ),blk_queue_get_max_sectors (q,req_op (rq))); }