Re: [PATCH 4/4] iomap: Use FUA for pure data O_DSYNC DIO writes

[Christoph Hellwig <hch@infradead.org>]

On Sat, Apr 21, 2018 at 02:54:05PM +0200, Jan Kara wrote:
> > -		if (iocb->ki_flags & IOCB_DSYNC)
> > +		if (iocb->ki_flags & IOCB_DSYNC) {
> >  			dio->flags |= IOMAP_DIO_NEED_SYNC;
> > +			/*
> > +			 * We optimistically try using FUA for this IO.  Any
> > +			 * non-FUA write that occurs will clear this flag, hence
> > +			 * we know before completion whether a cache flush is
> > +			 * necessary.
> > +			 */
> > +			dio->flags |= IOMAP_DIO_WRITE_FUA;
> > +		}
> 
> So I don't think this is quite correct. IOCB_DSYNC gets set also for O_SYNC
> writes (in that case we also set IOCB_SYNC). And for those we cannot use
> the FUA optimization AFAICT (definitely IOMAP_F_DIRTY isn't a safe
> indicator of a need of full fsync for O_SYNC). Other than that the patch
> looks good to me.

Oops, good catch. I think the above if should just be

		if (iocb->ki_flags & (IOCB_DSYNC | IOCB_SYNC) == IOCB_DSYNC)) {

and we are fine. 

> 
> 								Honza
> -- 
> Jan Kara <jack@suse.com>
> SUSE Labs, CR
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