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Re: [RFC] unifying write variants for filesystems

To: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Subject: Re: [RFC] unifying write variants for filesystems
From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Date: Sun, 2 Feb 2014 19:23:06 +0000
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>, Jens Axboe <axboe@xxxxxxxxx>, Mark Fasheh <mfasheh@xxxxxxxx>, Joel Becker <jlbec@xxxxxxxxxxxx>, linux-fsdevel <linux-fsdevel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx, Sage Weil <sage@xxxxxxxxxxx>, Steve French <sfrench@xxxxxxxxx>, Dave Kleikamp <shaggy@xxxxxxxxxx>, Anton Altaparmakov <anton@xxxxxxxxxx>, Miklos Szeredi <miklos@xxxxxxxxxx>
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In-reply-to: <20140202192104.GA21959@xxxxxxxxxxxxxxxxxx>
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Sender: Al Viro <viro@xxxxxxxxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Sun, Feb 02, 2014 at 07:21:04PM +0000, Al Viro wrote:
> BTW, is there any reason why fuse/dev.c doesn't use atomic kmaps for
> everything?  After all, as soon as we'd done kmap() in there, we
> grab a spinlock and don't drop it until just before kunmap().  With
> nothing by memcpy() done in between...  Miklos?  AFAICS, we only win

s/by/but/ - sorry...

> from switching to kmap_atomic there - we can't block anyway, we don't
> need it to be visible on other CPUs and nesting isn't a problem.
> Looks like it'll be cheaper in highmem cases and do exactly the same
> thing as now for non-highmem...  Comments?
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