Messages in this thread | | | Date | Fri, 27 Jan 2006 13:06:27 -0600 | From | Mike Christie <> | Subject | Re: More information on scsi_cmd_cache leak... (bisect) |
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Jens Axboe wrote: > On Fri, Jan 27 2006, Jens Axboe wrote: > >>On Fri, Jan 27 2006, Neil Brown wrote: >> >>>On Friday January 27, chase.venters@clientec.com 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. > > > Sorry, that was for the ->issue_flush() that md also does but did before > the barrier addition as well. Most of the barrier handling is done in > the block layer, but it could show leaks in SCSI of course. FWIW, I > tested barriers with and without md on SCSI here a few days ago and > didn't see any leaks at all. >
It does not have anything to do with this in scsi_io_completion does it?
if (blk_complete_barrier_rq(q, req, good_bytes >> 9)) return;
For that case the scsi_cmnd does not get freed. Does it come back around again and get released from a different path? - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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