From: Dave Chinner <david@fromorbit.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>,
Matthew Wilcox <willy@infradead.org>,
Jens Axboe <axboe@kernel.dk>,
linux-block@vger.kernel.org,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Dave Chinner <dchinner@redhat.com>,
Linux FS Devel <linux-fsdevel@vger.kernel.org>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
linux-xfs@vger.kernel.org, Bart Van Assche <bvanassche@acm.org>
Subject: Re: [PATCH 4/5] block: introduce helpers for allocating IO buffers from slab
Date: Fri, 19 Oct 2018 16:43:19 +1100 [thread overview]
Message-ID: <20181019054319.GL6311@dastard> (raw)
In-Reply-To: <20181019025348.GB14531@ming.t460p>
On Fri, Oct 19, 2018 at 10:53:49AM +0800, Ming Lei wrote:
> On Thu, Oct 18, 2018 at 05:22:19PM +0200, Christoph Hellwig wrote:
> > On Thu, Oct 18, 2018 at 08:11:23AM -0700, Matthew Wilcox wrote:
> > > On Thu, Oct 18, 2018 at 04:42:07PM +0200, Christoph Hellwig wrote:
> > > > This all seems quite complicated.
> > > >
> > > > I think the interface we'd want is more one that has a little
> > > > cache of a single page in the queue, and a little bitmap which
> > > > sub-page size blocks of it are used.
> > > >
> > > > Something like (pseudo code minus locking):
> > > >
> > > > void *blk_alloc_sector_buffer(struct block_device *bdev, gfp_t gfp)
> > > > {
> > > > unsigned block_size = block_size(bdev);
> > > >
> > > > if (blocksize >= PAGE_SIZE)
> > > > return (void *)__get_free_pages(gfp, get_order(blocksize));
> > > >
> > > > if (bdev->fragment_cache_page) {
> > > > [ <find fragment in bdev->fragment_cache_page using
> > > > e.g. bitmap and return if found]
> > > > }
> > > >
> > > > bdev->fragment_cache_page = (void *)__get_free_page(gfp);
> > > > goto find_again;
> > > > }
> > >
> > > This looks a lot like page_frag_alloc() except I think page_frag_alloc()
> > > may be more efficient.
> >
> > Oh, nice. Sounds like XFS should just use page_frag_alloc. I'll give
> > it a spin.
>
> XFS or other fs can use page_frag_alloc() directly, seems not necessary to
> introduce this change in block layer any more given 512-aligned buffer
> should be fine everywhere.
>
> The only benefit to make it as block helper is that the offset or size
> can be checked with q->dma_alignment.
>
> Dave/Jens, do you think which way is better? Put allocation as block
> helper or fs uses page_frag_alloc() directly for allocating 512*N-byte
> buffer(total size is less than PAGE_SIZE)?
Cristoph has already said he's looking at using page_frag_alloc()
directly in XFS....
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2018-10-19 13:47 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-18 13:18 [PATCH 0/5] block: introduce helpers for allocating io buffer from slab Ming Lei
2018-10-18 13:18 ` [PATCH 1/5] block: warn on un-aligned DMA IO buffer Ming Lei
2018-10-18 14:27 ` Jens Axboe
2018-10-18 14:43 ` Christoph Hellwig
2018-10-18 14:46 ` Jens Axboe
2018-10-19 1:28 ` Ming Lei
2018-10-19 1:33 ` Jens Axboe
2018-10-19 1:39 ` Ming Lei
2018-10-19 1:52 ` Jens Axboe
2018-10-19 2:06 ` Ming Lei
2018-10-19 2:10 ` Jens Axboe
2018-10-18 14:28 ` Christoph Hellwig
2018-10-18 13:18 ` [PATCH 2/5] block: move .dma_alignment into q->limits Ming Lei
2018-10-18 14:29 ` Christoph Hellwig
2018-10-18 20:36 ` Bart Van Assche
2018-10-18 13:18 ` [PATCH 3/5] block: make dma_alignment as stacked limit Ming Lei
2018-10-18 14:31 ` Christoph Hellwig
2018-10-18 13:18 ` [PATCH 4/5] block: introduce helpers for allocating IO buffers from slab Ming Lei
2018-10-18 14:42 ` Christoph Hellwig
2018-10-18 15:11 ` Matthew Wilcox
2018-10-18 15:22 ` Christoph Hellwig
2018-10-19 2:53 ` Ming Lei
2018-10-19 4:06 ` Jens Axboe
2018-10-19 5:43 ` Dave Chinner [this message]
2018-10-18 13:18 ` [PATCH 5/5] xfs: use block layer helpers to allocate io buffer " Ming Lei
2018-10-18 14:03 ` [PATCH 0/5] block: introduce helpers for allocating " Matthew Wilcox
2018-10-18 14:05 ` Christoph Hellwig
2018-10-18 15:06 ` Matthew Wilcox
2018-10-18 15:21 ` Christoph Hellwig
2018-10-18 15:50 ` Bart Van Assche
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