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Message-ID: <20151116224222.GW19199@dastard>
Date: Tue, 17 Nov 2015 09:42:22 +1100
From: Dave Chinner <david@...morbit.com>
To: Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc: linux-kernel@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>,
"J. Bruce Fields" <bfields@...ldses.org>,
Theodore Ts'o <tytso@....edu>,
Alexander Viro <viro@...iv.linux.org.uk>,
Andreas Dilger <adilger.kernel@...ger.ca>,
Dan Williams <dan.j.williams@...el.com>,
Ingo Molnar <mingo@...hat.com>, Jan Kara <jack@...e.com>,
Jeff Layton <jlayton@...chiereds.net>,
Matthew Wilcox <willy@...ux.intel.com>,
Thomas Gleixner <tglx@...utronix.de>,
linux-ext4@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-nvdimm@...ts.01.org, x86@...nel.org,
xfs@....sgi.com, Andrew Morton <akpm@...ux-foundation.org>,
Matthew Wilcox <matthew.r.wilcox@...el.com>,
Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH v2 07/11] mm: add find_get_entries_tag()
On Fri, Nov 13, 2015 at 05:06:46PM -0700, Ross Zwisler wrote:
> Add find_get_entries_tag() to the family of functions that include
> find_get_entries(), find_get_pages() and find_get_pages_tag(). This is
> needed for DAX dirty page handling because we need a list of both page
> offsets and radix tree entries ('indices' and 'entries' in this function)
> that are marked with the PAGECACHE_TAG_TOWRITE tag.
>
> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> ---
> include/linux/pagemap.h | 3 +++
> mm/filemap.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 64 insertions(+)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index a6c78e0..6fea3be 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -354,6 +354,9 @@ unsigned find_get_pages_contig(struct address_space *mapping, pgoff_t start,
> unsigned int nr_pages, struct page **pages);
> unsigned find_get_pages_tag(struct address_space *mapping, pgoff_t *index,
> int tag, unsigned int nr_pages, struct page **pages);
> +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> + int tag, unsigned int nr_entries,
> + struct page **entries, pgoff_t *indices);
>
> struct page *grab_cache_page_write_begin(struct address_space *mapping,
> pgoff_t index, unsigned flags);
> diff --git a/mm/filemap.c b/mm/filemap.c
> index d5e94fd..89ab448 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1454,6 +1454,67 @@ repeat:
> }
> EXPORT_SYMBOL(find_get_pages_tag);
>
> +/**
> + * find_get_entries_tag - find and return entries that match @tag
> + * @mapping: the address_space to search
> + * @start: the starting page cache index
> + * @tag: the tag index
> + * @nr_entries: the maximum number of entries
> + * @entries: where the resulting entries are placed
> + * @indices: the cache indices corresponding to the entries in @entries
> + *
> + * Like find_get_entries, except we only return entries which are tagged with
> + * @tag.
> + */
> +unsigned find_get_entries_tag(struct address_space *mapping, pgoff_t start,
> + int tag, unsigned int nr_entries,
> + struct page **entries, pgoff_t *indices)
> +{
> + void **slot;
> + unsigned int ret = 0;
> + struct radix_tree_iter iter;
> +
> + if (!nr_entries)
> + return 0;
> +
> + rcu_read_lock();
> +restart:
> + radix_tree_for_each_tagged(slot, &mapping->page_tree,
> + &iter, start, tag) {
> + struct page *page;
> +repeat:
> + page = radix_tree_deref_slot(slot);
> + if (unlikely(!page))
> + continue;
> + if (radix_tree_exception(page)) {
> + if (radix_tree_deref_retry(page))
> + goto restart;
That restart condition looks wrong. ret can be non-zero, but we
start looking from the original start index again, resulting in
duplicates being added to the return arrays...
Cheers,
Dave.
--
Dave Chinner
david@...morbit.com
--
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