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From: David Howells <dhowells@redhat.com>
To: Jeff Layton <jlayton@kernel.org>
Cc: dhowells@redhat.com, linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	Christoph Hellwig <hch@lst.de>,
	linux-mm@kvack.org, linux-cachefs@redhat.com,
	linux-afs@lists.infradead.org, linux-nfs@vger.kernel.org,
	linux-cifs@vger.kernel.org, ceph-devel@vger.kernel.org,
	v9fs-developer@lists.sourceforge.net,
	Trond Myklebust <trond.myklebust@hammerspace.com>,
	Anna Schumaker <anna.schumaker@netapp.com>,
	Steve French <sfrench@samba.org>,
	Dominique Martinet <asmadeus@codewreck.org>,
	David Wysochanski <dwysocha@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH v6 01/30] iov_iter: Add ITER_XARRAY
Date: Thu, 22 Apr 2021 14:51:32 +0100	[thread overview]
Message-ID: <2293710.1619099492@warthog.procyon.org.uk> (raw)
In-Reply-To: <27c369a8f42bb8a617672b2dc0126a5c6df5a050.camel@kernel.org>

Jeff Layton <jlayton@kernel.org> wrote:

> As a general note, iov_iter.c could really do with some (verbose)
> comments explaining things. A kerneldoc header that explains the
> arguments to iterate_all_kinds would sure make this easier to review.

Definitely.  But that really requires a separate patch.

> > @@ -1126,7 +1199,12 @@ void iov_iter_revert(struct iov_iter *i, size_t unroll)
> >  		return;
> >  	}
> >  	unroll -= i->iov_offset;
> > -	if (iov_iter_is_bvec(i)) {
> > +	if (iov_iter_is_xarray(i)) {
> > +		BUG(); /* We should never go beyond the start of the specified
> > +			* range since we might then be straying into pages that
> > +			* aren't pinned.
> > +			*/
> 
> It's not needed now, but there are a lot of calls to iov_iter_revert in
> the kernel, and going backward doesn't necessarily mean we'd be straying
> into an unpinned range. xarray_start never changes; would it not be ok
> to allow reverting as long as you don't move to a lower offset than that
> point?

This is handled starting a couple of lines above the start of the hunk:

	if (unroll <= i->iov_offset) {
		i->iov_offset -= unroll;
		return;
	}

As long as the amount you want to unroll by doesn't exceed the amount you've
consumed of the iterator, it will allow you to do it.  The BUG is there to
catch someone attempting to over-revert (and there's no way to return an
error).

> > +static ssize_t iter_xarray_copy_pages(struct page **pages, struct xarray *xa,
> > +				       pgoff_t index, unsigned int nr_pages)
> 
> nit: This could use a different name -- I was expecting to see page
> _contents_ copied here, but it's just populating the page array with
> pointers.

Fair point.  Um...  how about iter_xarray_populate_pages() or
iter_xarray_list_pages()?

> I think you've planned to remove iov_iter_for_each_range as well? I'll
> assume that this is going away. It might be nice to post the latest
> version of this patch with that change, just for posterity.

I'll put that in a separate patch.

> In any case, this all looks reasonable to me, modulo a few nits and a
> general dearth of comments.
> 
> Reviewed-by: Jeff Layton <jlayton@kernel.org>

Thanks,
David


  parent reply	other threads:[~2021-04-22 13:51 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-08 14:03 [PATCH v6 00/30] Network fs helper library & fscache kiocb API David Howells
2021-04-08 14:04 ` [PATCH v6 01/30] iov_iter: Add ITER_XARRAY David Howells
2021-04-09  1:24   ` Al Viro
2021-04-09 18:10     ` [RFC PATCH 1/2] iov_iter: Remove iov_iter_for_each_range() David Howells
2021-04-09 18:11     ` [RFC PATCH 2/2] iov_iter: Drop the X argument from iterate_all_kinds() and use B instead David Howells
2021-04-09  9:09   ` [PATCH v6 01/30] iov_iter: Add ITER_XARRAY David Howells
2021-04-09 11:44     ` Matthew Wilcox
2021-04-22 13:35   ` Jeff Layton
2021-04-22 13:51   ` David Howells [this message]
2021-04-22 14:51     ` Jeff Layton
2021-04-08 14:04 ` [PATCH v6 02/30] mm: Add set/end/wait functions for PG_private_2 David Howells
2021-04-08 14:50   ` Matthew Wilcox
2021-04-08 15:25   ` David Howells
2021-04-08 15:57   ` David Howells
2021-04-08 21:15   ` [RFC][PATCH] mm: Split page_has_private() in two to better handle PG_private_2 David Howells
2021-04-08 23:50     ` Linus Torvalds
2021-04-09 10:59       ` [RFC PATCH 1/3] Make the generic bitops return bool David Howells
2021-04-09 10:59       ` [RFC PATCH 2/3] mm: Return bool from pagebit test functions David Howells
2021-04-09 11:16         ` Matthew Wilcox
2021-04-09 12:00         ` David Howells
2021-04-09 12:35         ` David Howells
2021-04-09 16:03         ` David Howells
2021-04-09 10:59       ` [RFC PATCH 3/3] mm: Split page_has_private() in two to better handle PG_private_2 David Howells
2021-04-09 11:24         ` Matthew Wilcox
2021-04-09  8:14     ` [RFC][PATCH] " David Howells
2021-04-13 15:11   ` [PATCH v7] mm: Add set/end/wait functions for PG_private_2 David Howells
2021-04-13 15:22     ` Matthew Wilcox
2021-04-08 14:04 ` [PATCH v6 03/30] mm/filemap: Pass the file_ra_state in the ractl David Howells
2021-04-08 14:04 ` [PATCH v6 04/30] fs: Document file_ra_state David Howells
2021-04-08 14:04 ` [PATCH v6 05/30] mm: Implement readahead_control pageset expansion David Howells
2021-04-08 14:55   ` Matthew Wilcox
2021-04-08 14:05 ` [PATCH v6 06/30] netfs: Make a netfs helper module David Howells
2021-04-08 14:05 ` [PATCH v6 07/30] netfs: Documentation for helper library David Howells
2021-04-08 14:05 ` [PATCH v6 08/30] netfs, mm: Move PG_fscache helper funcs to linux/netfs.h David Howells
2021-04-08 14:05 ` [PATCH v6 09/30] netfs, mm: Add set/end/wait_on_page_fscache() aliases David Howells
2021-04-08 14:06 ` [PATCH v6 10/30] netfs: Provide readahead and readpage netfs helpers David Howells
2021-04-08 14:06 ` [PATCH v6 11/30] netfs: Add tracepoints David Howells
2021-04-08 14:06 ` [PATCH v6 12/30] netfs: Gather stats David Howells
2021-04-08 14:06 ` [PATCH v6 13/30] netfs: Add write_begin helper David Howells
2021-04-08 14:06 ` [PATCH v6 14/30] netfs: Define an interface to talk to a cache David Howells
2021-04-08 14:07 ` [PATCH v6 15/30] netfs: Add a tracepoint to log failures that would be otherwise unseen David Howells
2021-04-08 14:07 ` [PATCH v6 16/30] fscache, cachefiles: Add alternate API to use kiocb for read/write to cache David Howells
2021-04-08 14:07 ` [PATCH v6 17/30] afs: Disable use of the fscache I/O routines David Howells
2021-04-08 14:07 ` [PATCH v6 18/30] afs: Pass page into dirty region helpers to provide THP size David Howells
2021-04-08 14:08 ` [PATCH v6 19/30] afs: Print the operation debug_id when logging an unexpected data version David Howells
2021-04-08 14:08 ` [PATCH v6 20/30] afs: Move key to afs_read struct David Howells
2021-04-08 14:08 ` [PATCH v6 21/30] afs: Don't truncate iter during data fetch David Howells
2021-04-08 14:08 ` [PATCH v6 22/30] afs: Log remote unmarshalling errors David Howells
2021-04-08 14:08 ` [PATCH v6 23/30] afs: Set up the iov_iter before calling afs_extract_data() David Howells
2021-04-08 14:09 ` [PATCH v6 24/30] afs: Use ITER_XARRAY for writing David Howells
2021-04-08 14:09 ` [PATCH v6 25/30] afs: Wait on PG_fscache before modifying/releasing a page David Howells
2021-04-08 14:09 ` [PATCH v6 26/30] afs: Extract writeback extension into its own function David Howells
2021-04-08 14:09 ` [PATCH v6 27/30] afs: Prepare for use of THPs David Howells
2021-04-08 14:09 ` [PATCH v6 28/30] afs: Use the fs operation ops to handle FetchData completion David Howells
2021-04-08 14:10 ` [PATCH v6 29/30] afs: Use new netfs lib read helper API David Howells
2021-04-08 14:10 ` [PATCH v6 30/30] afs: Use the netfs_write_begin() helper David Howells
2021-04-08 15:40 ` [PATCH v6 00/30] Network fs helper library & fscache kiocb API Jeff Layton
2021-04-09 12:04 ` David Wysochanski
2021-04-13 14:56   ` David Wysochanski
2021-04-13 16:21 ` Marc Dionne

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