lkml.org 
[lkml]   [2011]   [Nov]   [28]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[RFC PATCH] block: change max_segments default to USHRT_MAX
Date
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


\
 
 \ /
  Last update: 2011-11-28 23:03    [W:0.051 / U:0.252 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site