| Message ID | 1447459610-14259-8-git-send-email-ross.zwisler@linux.intel.com |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
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@linux.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.
On Tue, Nov 17, 2015 at 09:42:22AM +1100, Dave Chinner wrote: > 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@linux.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... This same restart logic is used in all the functions in this family: find_get_entry() (though the tag is "repeat"), find_get_entries(), find_get_pages(), find_get_pages_contig() and find_get_pages_tag(). Most don't have it well commented, but there is a good comment in find_get_pages(): 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. */ WARN_ON(iter.index); goto restart; } I think the logic is correct, but I'm happy to add this comment in find_get_entries_tag() if it would make things clearer. -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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; + /* + * 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); + /* * CD/DVDs are error prone. When a medium error occurs, the driver may fail * a _large_ part of the i/o request. Imagine the worst scenario:
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@linux.intel.com> --- include/linux/pagemap.h | 3 +++ mm/filemap.c | 61 +++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 64 insertions(+)