Re: Large amount of scsi-sgpool objects

James Bottomley
2009-03-03T16:25:31Z

On Tue, 2009-03-03 at 17:08 +0100, Jan Engelhardt wrote:
> 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:

OK, this is a bad patch, so just revert it. It was posted to linux-scsi
initially in this form before the author posted a new one with the
missing release buffers added. It looks like the first incarnation got
pulled into the -rt tree for some reasons.

So the real question is why does the -rt tree even have patches not in
the vanilla SCSI tree? This type of cockup clearly demonstrates why
it's a bad idea.

James

> 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