Re: [PATCH] xfs: allocate sector sized IO buffer via page_frag_alloc

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On Tue, Feb 26, 2019 at 08:35:46PM +0800, Ming Lei wrote:
> On Tue, Feb 26, 2019 at 04:12:09AM -0800, Matthew Wilcox wrote:
> > On Tue, Feb 26, 2019 at 07:12:49PM +0800, Ming Lei wrote:
> > > The buffer needs to be device block size aligned for dio, and now the block
> > > size can be 512, 1024, 2048 and 4096.
> > 
> > Why does the block size make a difference?  This requirement is due to
> > some storage devices having shoddy DMA controllers.  Are you saying there
> > are devices which can't even do 512-byte aligned I/O?
> 
> Direct IO requires that, see do_blockdev_direct_IO().
> 
> This issue can be triggered when running xfs over loop/dio. We could
> fallback to buffered IO under this situation, but not sure it is the
> only case.

Wait, we're imposing a ridiculous amount of complexity on XFS for no
reason at all?  We should just change this to 512-byte alignment.  Tying
it to the blocksize of the device never made any sense.



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