linux-kernel - Re: New TRIM/UNMAP tree published (2009-05-02)

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Date:	Sun, 3 May 2009 08:48:47 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Matthew Wilcox <willy@...ux.intel.com>,
	Boaz Harrosh <bharrosh@...asas.com>, linux-ide@...r.kernel.org,
	linux-kernel@...r.kernel.org, Jeff Garzik <jgarzik@...hat.com>,
	linux-scsi@...r.kernel.org, Jens Axboe <jens.axboe@...cle.com>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Mark Lord <lkml@....ca>
Subject: Re: New TRIM/UNMAP tree published (2009-05-02)

On Sun, May 03, 2009 at 02:07:32PM +0100, Hugh Dickins wrote:
> I notice OCZ hope to have updated Vertex firmware mid-May,
> such that their TRIM support matches up with (y)ours.

Excellent.

> You have GFP_KERNEL allocations in your discard_fn()s.  I believe that
> allocations down at that level will need to be GFP_NOIO - the bio mempool
> might be empty by this point, you don't want memory allocation to get into
> submitting even more I/O to satisfy your discard_fn().  Does it need its
> own mempool of reserve pages?  My guess is that you can get away without
> that, since a failed discard, though regrettable, loses no data.

You make a good point.  There's definitely still work to be done around
error handling.  OTOH, we could always do what IDE does ...

static void idedisk_prepare_flush(struct request_queue *q, struct request *rq)
{
        ide_drive_t *drive = q->queuedata;
        struct ide_cmd *cmd = kmalloc(sizeof(*cmd), GFP_ATOMIC);

        /* FIXME: map struct ide_taskfile on rq->cmd[] */
        BUG_ON(cmd == NULL);



-- 
Matthew Wilcox				Intel Open Source Technology Centre
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."
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