Re: Large amount of scsi-sgpool objects

[James Bottomley <James.Bottomley@HansenPartnership.com>]

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