Messages in this thread Patch in this message | | | From | Mike Snitzer <> | Subject | [RFC PATCH] block: change max_segments default to USHRT_MAX | Date | Mon, 28 Nov 2011 17:00:15 -0500 |
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The reported problem was that a DM multipath device's max_segemnts was constrained to BLK_MAX_SEGMENTS (128) even though the underlying paths' max_segments were larger. For example, SCSI establishes a max_segments of SCSI_MAX_SG_CHAIN_SEGMENTS (2048).
If blk_set_default_limits() sets a block limit's value that is less than the possible range of values for that limit, stacked devices will never properly stack the affected limit via blk_stack_limits() if min_not_zero() is used.
BLK_MAX_SEGMENTS (128) is not the maximum value that may be established for the max_segments limit. Setting max_segments to a default of USHRT_MAX (65535) allows for proper stacking. Device drivers use blk_queue_max_segments() to override this default.
Reported-by: Shuichi Ihara <sihara@ddn.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com> --- block/blk-settings.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)
[NOTE: I avoided changing BLK_MAX_SEGMENTS to 2048 or USHRT_MAX but that may be the more appropriate fix. Or splitting BLK_MAX_SEGMENTS to BLK_DEF_MAX_SEGMENTS=2048 and BLK_SAFE_MAX_SEGMENTS=128.]
diff --git a/block/blk-settings.c b/block/blk-settings.c index fa1eb04..0ec98e0 100644 --- a/block/blk-settings.c +++ b/block/blk-settings.c @@ -110,7 +110,7 @@ EXPORT_SYMBOL_GPL(blk_queue_lld_busy); */ void blk_set_default_limits(struct queue_limits *lim) { - lim->max_segments = BLK_MAX_SEGMENTS; + lim->max_segments = USHRT_MAX; lim->max_integrity_segments = 0; lim->seg_boundary_mask = BLK_SEG_BOUNDARY_MASK; lim->max_segment_size = BLK_MAX_SEGMENT_SIZE; -- 1.7.4.4
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