Re: Large amount of scsi-sgpool objects

Jan Engelhardt
2009-03-03T16:08:00Z

On Tuesday 2009-03-03 16:21, James Bottomley wrote:
>> > $ slabtop
>> > OBJS ACTIVE USE OBJ SIZE SLABS OBJ/SLAB CACHE SIZE NAME
>> > 818616 818616 100% 0.16K 34109 24 136436K sgpool-8
>> > 253692 253692 100% 0.62K 42282 6 169128K sgpool-32
>> > 52017 52016 99% 2.50K 17339 3 138712K sgpool-128
>> > 26220 26219 99% 0.31K 2185 12 8740K sgpool-16
>> > 8927 8574 96% 0.03K 79 113 316K size-32
>>
>> Looks like a leak, by failing to call scsi_release_buffers()
>> somehow. (Which was changed recently)
>
>Firstly, I have to say I don't see this in the mainline tree, so could
>you try that with your setup just to verify (git head at 2.6.29-rc6).

Yes, looking at the rt patch (in broken-out it's in origin.diff),
it seems a bit obvious - the scsi_release_buffers is not called anymore:

diff --git a/drivers/scsi/scsi_lib.c b/drivers/scsi/scsi_lib.c
index 940dc32..d4c6ac3 100644
--- a/drivers/scsi/scsi_lib.c
+++ b/drivers/scsi/scsi_lib.c
@@ -703,71 +703,6 @@ void scsi_run_host_queues(struct Scsi_Host *shost)

static void __scsi_release_buffers(struct scsi_cmnd *, int);

-/*
- * Function: scsi_end_request()
- *
- * Purpose: Post-processing of completed commands (usually invoked at end
- * of upper level post-processing and scsi_io_completion).
- *
- * Arguments: cmd - command that is complete.
- * error - 0 if I/O indicates success, < 0 for I/O error.
- * bytes - number of bytes of completed I/O
- * requeue - indicates whether we should requeue leftovers.
- *
- * Lock status: Assumed that lock is not held upon entry.
- *
- * Returns: cmd if requeue required, NULL otherwise.
- *
- * Notes: This is called for block device requests in order to
- * mark some number of sectors as complete.
- *
- * We are guaranteeing that the request queue will be goosed
- * at some point during this call.
- * Notes: If cmd was requeued, upon return it will be a stale pointer.
- */
-static struct scsi_cmnd *scsi_end_request(struct scsi_cmnd *cmd, int error,
- int bytes, int requeue)
-{
- struct request_queue *q = cmd->device->request_queue;
- struct request *req = cmd->request;
-
- /*
- * If there are blocks left over at the end, set up the command
- * to queue the remainder of them.
- */
- if (blk_end_request(req, error, bytes)) {
- int leftover = (req->hard_nr_sectors << 9);
-
- if (blk_pc_request(req))
- leftover = req->data_len;
-
- /* kill remainder if no retrys */
- if (error && scsi_noretry_cmd(cmd))
- blk_end_request(req, error, leftover);
- else {
- if (requeue) {
- /*
- * Bleah. Leftovers again. Stick the
- * leftovers in the front of the
- * queue, and goose the queue again.
- */
- scsi_release_buffers(cmd);
- scsi_requeue_command(q, cmd);
- cmd = NULL;
- }
- return cmd;
- }
- }
-
- /*
- * This will goose the queue request function at the end, so we don't
- * need to worry about launching another command.
- */
- __scsi_release_buffers(cmd, 0);
- scsi_next_command(cmd);
- return NULL;
-}
-
static inline unsigned int scsi_sgtable_index(unsigned short nents)
{
unsigned int index;
@@ -929,7 +864,6 @@ static void scsi_end_bidi_request(struct scsi_cmnd *cmd)
void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
{
int result = cmd->result;
- int this_count;
struct request_queue *q = cmd->device->request_queue;
struct request *req = cmd->request;
int error = 0;
@@ -980,18 +914,30 @@ void scsi_io_completion(struct scsi_cmnd *cmd, unsigned int good_bytes)
SCSI_LOG_HLCOMPLETE(1, printk("%ld sectors total, "
"%d bytes done.\n",
req->nr_sectors, good_bytes));
-
- /* A number of bytes were successfully read. If there
- * are leftovers and there is some kind of error
- * (result != 0), retry the rest.
- */
- if (scsi_end_request(cmd, error, good_bytes, result == 0) == NULL)
+ if (blk_end_request(req, error, good_bytes) == 0) {
+ /* This request is completely finished; start the next one */
+ scsi_next_command(cmd);
return;
- this_count = blk_rq_bytes(req);
+ }

error = -EIO;

- if (host_byte(result) == DID_RESET) {
+ /* The request isn't finished yet. Figure out what to do next. */
+ if (result == 0) {
+ /* No error, so carry out the remainder of the request.
+ * Failure to make forward progress counts against the
+ * the number of retries.
+ */
+ if (good_bytes > 0 || --req->retries >= 0)
+ action = ACTION_REPREP;
+ else {
+ action = ACTION_FAIL;
+ description = "Retries exhausted";
+ }
+ } else if (error && scsi_noretry_cmd(cmd)) {
+ /* Retrys are disallowed, so kill the remainder. */
+ action = ACTION_FAIL;
+ } else if (host_byte(result) == DID_RESET) {
/* Third party bus reset or reset for error recovery
* reasons. Just retry the command and see what
* happens.

Would you happen to know where I have to reinsert them in the
rt modification shown here?

>If this holds true, there must be a bad patch in the -rt tree. You
>should be able to diff scsi_lib.c to see if there's something missing.
>
>Finally, there are one or two drivers (SCSI target) that do their own
>buffer management, so what drivers are you using?

ata1.00: ATA-5: WDC WD400EB-00CPF0, 06.04G06, max UDMA/100
ata1.00: 78165360 sectors, multi 16: LBA
ata1.01: ATAPI: HL-DT-ST DVDRAM GSA-4160B, A301, max UDMA/66
ata1.00: configured for UDMA/100
ata1.01: configured for UDMA/66
scsi 0:0:0:0: Direct-Access ATA WDC WD400EB-00CP 06.0 PQ: 0 ANSI: 5
scsi 0:0:1:0: CD-ROM HL-DT-ST DVDRAM GSA-4160B A301 PQ: 0 ANSI: 5
ata2.00: ATA-7: DIAMOND 250G 2B5400, RAMB1TU0, max UDMA/133
ata2.00: 490234752 sectors, multi 16: LBA48
ata2.00: configured for UDMA/133
scsi 1:0:0:0: Direct-Access ATA DIAMOND 250G 2B RAMB PQ: 0 ANSI: 5

Jan