On Tue, Dec 8, 2015 at 11:18 AM, Ross Zwisler
<ross.zwisler@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> ---
> include/linux/pagemap.h | 3 +++
> mm/filemap.c | 68
> +++++++++++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 71 insertions(+)
>
> diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> index 26eabf5..4db0425 100644
> --- a/include/linux/pagemap.h
> +++ b/include/linux/pagemap.h
> @@ -361,6 +361,9 @@ 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 167a4d9..99dfbc9 100644
> --- a/mm/filemap.c
> +++ b/mm/filemap.c
> @@ -1498,6 +1498,74 @@ 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)) {
> + /*
> + * Transient condition which can only trigger
> + * when entry at index 0 moves out of or back
> + * to root: none yet gotten, safe to restart.
> + */
> + goto restart;
> + }
> +
> + /*
> + * A shadow entry of a recently evicted page, a swap
> + * entry from shmem/tmpfs or a DAX entry. Return it
> + * without attempting to raise page count.
> + */
> + goto export;
> + }
> + if (!page_cache_get_speculative(page))
> + goto repeat;
> +
> + /* Has the page moved? */
> + if (unlikely(page != *slot)) {
> + page_cache_release(page);
> + goto repeat;
> + }
> +export:
> + indices[ret] = iter.index;
> + entries[ret] = page;
> + if (++ret == nr_entries)
> + break;
> + }
> + rcu_read_unlock();
> + return ret;
> +}
> +EXPORT_SYMBOL(find_get_entries_tag);
> +
Why does this mostly duplicate find_get_entries()?
Surely find_get_entries() can be implemented as a special case of
find_get_entries_tag().
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