On Fri, Jan 27 2006, Neil Brown wrote: > On Friday January 27, chase.venters@xxxxxxxxxxxx wrote: > > Greetings, > > Just a quick recap - there are at least 4 reports of 2.6.15 users > > experiencing severe slab leaks with scsi_cmd_cache. It seems that a few of us > > have a board (Asus P5GDC-V Deluxe) in common. We seem to have raid in common. > > After dealing with this leak for a while, I decided to do some dancing around > > with git bisect. I've landed on a possible point of regression: > > > > commit: a9701a30470856408d08657eb1bd7ae29a146190 > > [PATCH] md: support BIO_RW_BARRIER for md/raid1 > > > > I spent about an hour and a half reading through the patch, trying to see if > > I could make sense of what might be wrong. The result (after I dug into the > > code to make a change I foolishly thought made sense) was a hung kernel. > > This is important because when I rebooted into the kernel that had been > > giving me trouble, it started an md resync and I'm now watching (at least > > during this resync) the slab usage for scsi_cmd_cache stay sane: > > > > turbotaz ~ # cat /proc/slabinfo | grep scsi_cmd_cache > > scsi_cmd_cache 30 30 384 10 1 : tunables 54 27 8 : > > slabdata 3 3 0 > > > > This suggests that the problem happens when a BIO_RW_BARRIER write is > sent to the device. With this patch, md flags all superblock writes > as BIO_RW_BARRIER However md is not so likely to update the superblock often > during a resync. > > There is a (rough) count of the number of superblock writes in the > "Events" counter which "mdadm -D" will display. > You could try collecting 'Events' counter together with the > 'active_objs' count from /proc/slabinfo and graph the pairs - see if > they are linear. > > I believe a BIO_RW_BARRIER is likely to send some sort of 'flush' > command to the device, and the driver for your particular device may > well be losing scsi_cmd_cache allocation when doing that, but I leave > that to someone how knows more about that code. I already checked up on that since I suspected barriers initially. The path there for scsi is sd.c:sd_issue_flush() which looks pretty straight forward. In the end it goes through the block layer and gets back to the SCSI layer as a regular REQ_BLOCK_PC request. -- Jens Axboe - : send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
