Re: [PATCH v2 4/5] swapfile: use ->read_iter and ->write_iter

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From: Omar Sandoval <osandov@osandov.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Trond Myklebust <trond.myklebust@primarydata.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
	Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v2 4/5] swapfile: use ->read_iter and ->write_iter
Date: Sun, 21 Dec 2014 23:32:34 -0800	[thread overview]
Message-ID: <20141222073234.GA14207@mew> (raw)
In-Reply-To: <20141220061337.GB22149@ZenIV.linux.org.uk>

On Sat, Dec 20, 2014 at 06:13:37AM +0000, Al Viro wrote:
> On Fri, Dec 19, 2014 at 07:18:28PM -0800, Omar Sandoval wrote:
> 
> > +		ret = swap_file->f_op->read_iter(&kiocb, &to);
> > +		if (ret == PAGE_SIZE) {
> > +			SetPageUptodate(page);
> >  			count_vm_event(PSWPIN);
> > +			ret = 0;
> > +		} else {
> > +			ClearPageUptodate(page);
> > +			SetPageError(page);
> > +		}
> > +		unlock_page(page);
> 
> Umm...  What's to guarantee that ->read_iter() won't try lock_page() on what
> turns out to be equal to page?

Ergh. I don't see why ->read_iter would be screwing around in the swap
cache or with the pages in the iterator, anything in particular you can
see happening?

-- 
Omar

WARNING: multiple messages have this Message-ID (diff)

From: Omar Sandoval <osandov-nWWhXC5lh1RBDgjK7y7TUQ@public.gmane.org>
To: Al Viro <viro-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>
Cc: Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Trond Myklebust
	<trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org>,
	Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	linux-fsdevel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org,
	linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Mel Gorman <mgorman-l3A5Bk7waGM@public.gmane.org>
Subject: Re: [PATCH v2 4/5] swapfile: use ->read_iter and ->write_iter
Date: Sun, 21 Dec 2014 23:32:34 -0800	[thread overview]
Message-ID: <20141222073234.GA14207@mew> (raw)
In-Reply-To: <20141220061337.GB22149-3bDd1+5oDREiFSDQTTA3OLVCufUGDwFn@public.gmane.org>

On Sat, Dec 20, 2014 at 06:13:37AM +0000, Al Viro wrote:
> On Fri, Dec 19, 2014 at 07:18:28PM -0800, Omar Sandoval wrote:
> 
> > +		ret = swap_file->f_op->read_iter(&kiocb, &to);
> > +		if (ret == PAGE_SIZE) {
> > +			SetPageUptodate(page);
> >  			count_vm_event(PSWPIN);
> > +			ret = 0;
> > +		} else {
> > +			ClearPageUptodate(page);
> > +			SetPageError(page);
> > +		}
> > +		unlock_page(page);
> 
> Umm...  What's to guarantee that ->read_iter() won't try lock_page() on what
> turns out to be equal to page?

Ergh. I don't see why ->read_iter would be screwing around in the swap
cache or with the pages in the iterator, anything in particular you can
see happening?

-- 
Omar
--
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WARNING: multiple messages have this Message-ID (diff)

From: Omar Sandoval <osandov@osandov.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Trond Myklebust <trond.myklebust@primarydata.com>,
	Christoph Hellwig <hch@infradead.org>,
	linux-fsdevel@vger.kernel.org, linux-mm@kvack.org,
	linux-nfs@vger.kernel.org, linux-kernel@vger.kernel.org,
	Mel Gorman <mgorman@suse.de>
Subject: Re: [PATCH v2 4/5] swapfile: use ->read_iter and ->write_iter
Date: Sun, 21 Dec 2014 23:32:34 -0800	[thread overview]
Message-ID: <20141222073234.GA14207@mew> (raw)
In-Reply-To: <20141220061337.GB22149@ZenIV.linux.org.uk>

On Sat, Dec 20, 2014 at 06:13:37AM +0000, Al Viro wrote:
> On Fri, Dec 19, 2014 at 07:18:28PM -0800, Omar Sandoval wrote:
> 
> > +		ret = swap_file->f_op->read_iter(&kiocb, &to);
> > +		if (ret == PAGE_SIZE) {
> > +			SetPageUptodate(page);
> >  			count_vm_event(PSWPIN);
> > +			ret = 0;
> > +		} else {
> > +			ClearPageUptodate(page);
> > +			SetPageError(page);
> > +		}
> > +		unlock_page(page);
> 
> Umm...  What's to guarantee that ->read_iter() won't try lock_page() on what
> turns out to be equal to page?

Ergh. I don't see why ->read_iter would be screwing around in the swap
cache or with the pages in the iterator, anything in particular you can
see happening?

-- 
Omar

--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
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next prev parent reply	other threads:[~2014-12-22  7:32 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-12-20  3:18 [PATCH v2 0/5] clean up and generalize swap-over-NFS Omar Sandoval
2014-12-20  3:18 ` Omar Sandoval
2014-12-20  3:18 ` [PATCH v2 1/5] iov_iter: add ITER_BVEC helpers Omar Sandoval
2014-12-20  3:18   ` Omar Sandoval
2014-12-20  3:18 ` [PATCH v2 2/5] direct-io: don't dirty ITER_BVEC pages on read Omar Sandoval
2014-12-20  3:18   ` Omar Sandoval
2014-12-20  6:01   ` Al Viro
2014-12-20  6:01     ` Al Viro
2014-12-22  7:12     ` Omar Sandoval
2014-12-22  7:12       ` Omar Sandoval
2014-12-20  3:18 ` [PATCH v2 3/5] nfs: don't dirty ITER_BVEC pages read through direct I/O Omar Sandoval
2014-12-20  3:18   ` Omar Sandoval
2015-01-05 14:41   ` Anna Schumaker
2015-01-05 14:41     ` Anna Schumaker
2015-01-05 14:41     ` Anna Schumaker
2015-01-08  9:25     ` Omar Sandoval
2015-01-08  9:25       ` Omar Sandoval
2015-01-08  9:25       ` Omar Sandoval
2014-12-20  3:18 ` [PATCH v2 4/5] swapfile: use ->read_iter and ->write_iter Omar Sandoval
2014-12-20  3:18   ` Omar Sandoval
2014-12-20  6:13   ` Al Viro
2014-12-20  6:13     ` Al Viro
2014-12-22  7:32     ` Omar Sandoval [this message]
2014-12-22  7:32       ` Omar Sandoval
2014-12-22  7:32       ` Omar Sandoval
2014-12-20  3:18 ` [PATCH v2 5/5] vfs: update swap_{,de}activate documentation Omar Sandoval
2014-12-20  3:18   ` Omar Sandoval
2015-01-14  3:18 ` [PATCH v2 0/5] clean up and generalize swap-over-NFS Omar Sandoval
2015-01-14  3:18   ` Omar Sandoval
2015-01-14  3:18   ` Omar Sandoval
2015-01-21 19:14   ` Omar Sandoval
2015-01-21 19:14     ` Omar Sandoval
2015-01-21 19:14     ` Omar Sandoval

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