[PATCH 0/3] smb3, afs: Revert changes to {cifs,afs}_writepages_region()

[PATCH 0/3] smb3, afs: Revert changes to {cifs,afs}_writepages_region()

[David Howells]

Hi Linus, Steve,

Could you consider applying these please?

I've split the patch that I proposed[1] to revert Vishal's patch to afs and
Linus's changes to cifs back to the point where find_get_pages_range_tag()
was being used to get a single folio and then replace that with a function,
filemap_get_folio_tag() that just gets a single folio and done some
benchmarking against this and some conversions to use write_cache_pages()
in various ways.

This is using the following to do testing of the write paths:

	fio --ioengine=libaio --direct=0 --gtod_reduce=1 --name=readtest \
	    --filename=/xfstest.test/foo --iodepth=128 --time_based \
	    --runtime=120 --readwrite=randread --iodepth_low=96 \
	    --iodepth_batch=16 --numjobs=4 --size=16M --bs=4k

The base for comparison, the upstream kernel at commit:

	d2980d8d826554fa6981d621e569a453787472f8
	"Merge tag 'mm-nonmm-stable-2023-02-20-15-29' of git://git./linux/kernel/git/akpm/mm"

plus the accumulated fixes on Steve's cifs for-next branch.

AFS firstly.  The code that's upstream keeps track of the dirtied region of
a folio in page->private, so I tried removing that to see what difference
it makes, in addition to trying conversions to use write_cache_pages().  I
also tried giving afs it's own copy of write_cache_pages() in order to
eliminate the function pointer - in case that had a signifcant effect due
to spectre mitigations.

  Base:
	WRITE: bw=302MiB/s (316MB/s), 71.9MiB/s-78.9MiB/s (75.3MB/s-82.8MB/s)
	WRITE: bw=303MiB/s (318MB/s), 65.9MiB/s-84.0MiB/s (69.1MB/s-88.1MB/s)
	WRITE: bw=310MiB/s (325MB/s), 73.6MiB/s-87.3MiB/s (77.1MB/s-91.5MB/s)

  Base + Partial revert (these patches):
	WRITE: bw=348MiB/s (365MB/s), 86.4MiB/s-87.5MiB/s (90.6MB/s-91.8MB/s)
	WRITE: bw=350MiB/s (367MB/s), 86.6MiB/s-88.4MiB/s (90.8MB/s-92.7MB/s)
	WRITE: bw=387MiB/s (406MB/s), 96.8MiB/s-97.0MiB/s (101MB/s-102MB/s)

  Base + write_cache_pages():
	WRITE: bw=280MiB/s (294MB/s), 69.7MiB/s-70.5MiB/s (73.0MB/s-73.9MB/s)
	WRITE: bw=285MiB/s (299MB/s), 70.9MiB/s-71.5MiB/s (74.4MB/s-74.9MB/s)
	WRITE: bw=290MiB/s (304MB/s), 71.6MiB/s-73.2MiB/s (75.1MB/s-76.8MB/s)

  Base + Page-dirty-region removed:
	WRITE: bw=301MiB/s (315MB/s), 70.4MiB/s-80.2MiB/s (73.8MB/s-84.1MB/s)
	WRITE: bw=325MiB/s (341MB/s), 78.5MiB/s-87.1MiB/s (82.3MB/s-91.3MB/s)
	WRITE: bw=320MiB/s (335MB/s), 71.6MiB/s-88.6MiB/s (75.0MB/s-92.9MB/s)

  Base + Page-dirty-region tracking removed +  write_cache_pages():
	WRITE: bw=288MiB/s (302MB/s), 71.9MiB/s-72.3MiB/s (75.4MB/s-75.8MB/s)
	WRITE: bw=284MiB/s (297MB/s), 70.7MiB/s-71.3MiB/s (74.1MB/s-74.8MB/s)
	WRITE: bw=287MiB/s (301MB/s), 71.2MiB/s-72.6MiB/s (74.7MB/s-76.1MB/s)

  Base + Page-dirty-region tracking removed + Own write_cache_pages()
	WRITE: bw=302MiB/s (316MB/s), 75.1MiB/s-76.1MiB/s (78.7MB/s-79.8MB/s)
	WRITE: bw=302MiB/s (316MB/s), 74.5MiB/s-76.1MiB/s (78.1MB/s-79.8MB/s)
	WRITE: bw=301MiB/s (316MB/s), 75.2MiB/s-75.5MiB/s (78.9MB/s-79.1MB/s)

So the partially reverted code appears significantly faster than code based
on write_cache_pages().  Removing the page-dirty-region tracking also slows
things down - I have a suspicion that this may be due to multipage folios
enlarging the apparently dirty regions of a file.

And then CIFS.  There's no dirtied region tracking here, so just the
partial reversion, a conversion to write_cache_pages() and its own version
of write_cache_pages() to eliminate the function pointer.

  Base:
	WRITE: bw=464MiB/s (487MB/s), 116MiB/s-116MiB/s (122MB/s-122MB/s)
	WRITE: bw=463MiB/s (486MB/s), 116MiB/s-116MiB/s (121MB/s-122MB/s)
	WRITE: bw=465MiB/s (488MB/s), 116MiB/s-116MiB/s (122MB/s-122MB/s)

  Base + Partial revert (these patches):
	WRITE: bw=470MiB/s (493MB/s), 117MiB/s-118MiB/s (123MB/s-123MB/s)
	WRITE: bw=467MiB/s (489MB/s), 117MiB/s-117MiB/s (122MB/s-122MB/s)
	WRITE: bw=464MiB/s (486MB/s), 116MiB/s-116MiB/s (121MB/s-122MB/s)

  Base + write_cache_pages():
	WRITE: bw=457MiB/s (479MB/s), 114MiB/s-114MiB/s (120MB/s-120MB/s)
	WRITE: bw=449MiB/s (471MB/s), 112MiB/s-113MiB/s (118MB/s-118MB/s)
	WRITE: bw=459MiB/s (482MB/s), 115MiB/s-115MiB/s (120MB/s-121MB/s)

  Base + Own write_cache_pages():
	WRITE: bw=451MiB/s (473MB/s), 113MiB/s-113MiB/s (118MB/s-118MB/s)
	WRITE: bw=455MiB/s (478MB/s), 114MiB/s-114MiB/s (119MB/s-120MB/s)
	WRITE: bw=453MiB/s (475MB/s), 113MiB/s-113MiB/s (119MB/s-119MB/s)
	WRITE: bw=459MiB/s (481MB/s), 115MiB/s-115MiB/s (120MB/s-120MB/s)

Here the partially reverted code appears slightly better - but the results
are very close so I'm not sure if it's statistically significant.

I've pushed the patches here also:

	https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=iov-cifs

David

Link: https://lore.kernel.org/r/2214157.1677250083@warthog.procyon.org.uk/ [1]

David Howells (3):
  mm: Add a function to get a single tagged folio from a file
  afs: Partially revert and use filemap_get_folio_tag()
  cifs: Partially revert and use filemap_get_folio_tag()

 fs/afs/write.c          | 118 +++++++++++++++++++---------------------
 fs/cifs/file.c          | 115 +++++++++++++++++----------------------
 include/linux/pagemap.h |   2 +
 mm/filemap.c            |  58 ++++++++++++++++++++
 4 files changed, 166 insertions(+), 127 deletions(-)

[PATCH 1/3] mm: Add a function to get a single tagged folio from a file

[David Howells]

Add a function to get a single tagged folio from a file rather than a batch
for use in afs and cifs where, in the common case, the batch is likely to
be rendered irrelevant by the {afs,cifs}_extend_writeback() function.

For filemap_get_folios_tag() to be of use, the batch has to be passed down,
and if it contains scattered, non-contiguous folios, these are likely to
end up being pinned by the batch for significant periods of time whilst I/O
is undertaken on earlier pages.

Further, for write_cache_pages() to be useful, it would need to wait for
PG_fscache which is used to indicate that I/O is in progress from a folio to
the cache - but it can't do this unconditionally as some filesystems, such
as btrfs, use PG_private_2 for other purposes.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: linux-afs@lists.infradead.org
cc: linux-cifs@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/2214157.1677250083@warthog.procyon.org.uk/
---
 include/linux/pagemap.h |  2 ++
 mm/filemap.c            | 58 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 0acb8e1fb7af..577535633006 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -741,6 +741,8 @@ unsigned filemap_get_folios_contig(struct address_space *mapping,
 		pgoff_t *start, pgoff_t end, struct folio_batch *fbatch);
 unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
 		pgoff_t end, xa_mark_t tag, struct folio_batch *fbatch);
+struct folio *filemap_get_folio_tag(struct address_space *mapping, pgoff_t *start,
+				    pgoff_t end, xa_mark_t tag);
 
 struct page *grab_cache_page_write_begin(struct address_space *mapping,
 			pgoff_t index);
diff --git a/mm/filemap.c b/mm/filemap.c
index 2723104cc06a..1b1e9c661018 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -2339,6 +2339,64 @@ unsigned filemap_get_folios_tag(struct address_space *mapping, pgoff_t *start,
 }
 EXPORT_SYMBOL(filemap_get_folios_tag);
 
+/**
+ * filemap_get_folio_tag - Get the first folio matching @tag
+ * @mapping:    The address_space to search
+ * @start:      The starting page index
+ * @end:        The final page index (inclusive)
+ * @tag:        The tag index
+ *
+ * Search for and return the first folios in the mapping starting at index
+ * @start and up to index @end (inclusive).  The folio is returned with an
+ * elevated reference count.
+ *
+ * If a folio is returned, it may start before @start; if it does, it will
+ * contain @start.  The folio may also extend beyond @end; if it does, it will
+ * contain @end.  If folios are added to or removed from the page cache while
+ * this is running, they may or may not be found by this call.
+ *
+ * Return: The folio that was found or NULL.  @start is also updated to index
+ * the next folio for the traversal or will be left pointing after @end.
+ */
+struct folio *filemap_get_folio_tag(struct address_space *mapping, pgoff_t *start,
+				    pgoff_t end, xa_mark_t tag)
+{
+	XA_STATE(xas, &mapping->i_pages, *start);
+	struct folio *folio;
+
+	rcu_read_lock();
+	while ((folio = find_get_entry(&xas, end, tag)) != NULL) {
+		/*
+		 * Shadow entries should never be tagged, but this iteration
+		 * is lockless so there is a window for page reclaim to evict
+		 * a page we saw tagged. Skip over it.
+		 */
+		if (xa_is_value(folio))
+			continue;
+
+		if (folio_test_hugetlb(folio))
+			*start = folio->index + 1;
+		else
+			*start = folio_next_index(folio);
+		goto out;
+	}
+
+	/*
+	 * We come here when there is no page beyond @end. We take care to not
+	 * overflow the index @start as it confuses some of the callers. This
+	 * breaks the iteration when there is a page at index -1 but that is
+	 * already broke anyway.
+	 */
+	if (end == (pgoff_t)-1)
+		*start = (pgoff_t)-1;
+	else
+		*start = end + 1;
+out:
+	rcu_read_unlock();
+	return folio;
+}
+EXPORT_SYMBOL(filemap_get_folio_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:

[PATCH 2/3] afs: Partially revert and use filemap_get_folio_tag()

[David Howells]

Partially revert the changes made by:

    acc8d8588cb7e3e64b0d2fa611dad06574cd67b1.
    afs: convert afs_writepages_region() to use filemap_get_folios_tag()

The issue is that filemap_get_folios_tag() gets a batch of pages at a time,
and then afs_writepages_region() goes through them one at a time, extends
each into an operation with as many pages as will fit using the loop in
afs_extend_writeback() and submits it - but, in the common case, this means
that the other pages in the batch already got annexed and processed in
afs_extend_writeback() and we end up doing duplicate processing.

Switching to write_cache_pages() isn't an immediate substitute as that
doesn't take account of PG_fscache (and this bit is used in other ways by
other filesystems).

So go back to finding the next folio from the VM one at a time and then
extending the op onwards.

Fixes: acc8d8588cb7 ("afs: convert afs_writepages_region() to use filemap_get_folios_tag()")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Steve French <sfrench@samba.org>
cc: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: linux-afs@lists.infradead.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/2214157.1677250083@warthog.procyon.org.uk/
---
 fs/afs/write.c | 118 ++++++++++++++++++++++++-------------------------
 1 file changed, 57 insertions(+), 61 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 571f3b9a417e..2ed76697be96 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -704,87 +704,83 @@ static int afs_writepages_region(struct address_space *mapping,
 				 bool max_one_loop)
 {
 	struct folio *folio;
-	struct folio_batch fbatch;
 	ssize_t ret;
-	unsigned int i;
-	int n, skips = 0;
+	int skips = 0;
 
 	_enter("%llx,%llx,", start, end);
-	folio_batch_init(&fbatch);
 
 	do {
 		pgoff_t index = start / PAGE_SIZE;
 
-		n = filemap_get_folios_tag(mapping, &index, end / PAGE_SIZE,
-					PAGECACHE_TAG_DIRTY, &fbatch);
-
-		if (!n)
+		folio = filemap_get_folio_tag(mapping, &index, end / PAGE_SIZE,
+					      PAGECACHE_TAG_DIRTY);
+		if (!folio)
 			break;
-		for (i = 0; i < n; i++) {
-			folio = fbatch.folios[i];
-			start = folio_pos(folio); /* May regress with THPs */
 
-			_debug("wback %lx", folio_index(folio));
+		start = folio_pos(folio); /* May regress with THPs */
 
-			/* At this point we hold neither the i_pages lock nor the
-			 * page lock: the page may be truncated or invalidated
-			 * (changing page->mapping to NULL), or even swizzled
-			 * back from swapper_space to tmpfs file mapping
-			 */
-			if (wbc->sync_mode != WB_SYNC_NONE) {
-				ret = folio_lock_killable(folio);
-				if (ret < 0) {
-					folio_batch_release(&fbatch);
-					return ret;
-				}
-			} else {
-				if (!folio_trylock(folio))
-					continue;
-			}
+		_debug("wback %lx", folio_index(folio));
 
-			if (folio->mapping != mapping ||
-			    !folio_test_dirty(folio)) {
-				start += folio_size(folio);
-				folio_unlock(folio);
-				continue;
+		/* At this point we hold neither the i_pages lock nor the
+		 * page lock: the page may be truncated or invalidated
+		 * (changing page->mapping to NULL), or even swizzled
+		 * back from swapper_space to tmpfs file mapping
+		 */
+		if (wbc->sync_mode != WB_SYNC_NONE) {
+			ret = folio_lock_killable(folio);
+			if (ret < 0) {
+				folio_put(folio);
+				return ret;
+			}
+		} else {
+			if (!folio_trylock(folio)) {
+				folio_put(folio);
+				return 0;
 			}
+		}
 
-			if (folio_test_writeback(folio) ||
-			    folio_test_fscache(folio)) {
-				folio_unlock(folio);
-				if (wbc->sync_mode != WB_SYNC_NONE) {
-					folio_wait_writeback(folio);
+		if (folio_mapping(folio) != mapping ||
+		    !folio_test_dirty(folio)) {
+			start += folio_size(folio);
+			folio_unlock(folio);
+			folio_put(folio);
+			continue;
+		}
+
+		if (folio_test_writeback(folio) ||
+		    folio_test_fscache(folio)) {
+			folio_unlock(folio);
+			if (wbc->sync_mode != WB_SYNC_NONE) {
+				folio_wait_writeback(folio);
 #ifdef CONFIG_AFS_FSCACHE
-					folio_wait_fscache(folio);
+				folio_wait_fscache(folio);
 #endif
-				} else {
-					start += folio_size(folio);
-				}
-				if (wbc->sync_mode == WB_SYNC_NONE) {
-					if (skips >= 5 || need_resched()) {
-						*_next = start;
-						_leave(" = 0 [%llx]", *_next);
-						return 0;
-					}
-					skips++;
-				}
-				continue;
+			} else {
+				start += folio_size(folio);
 			}
-
-			if (!folio_clear_dirty_for_io(folio))
-				BUG();
-			ret = afs_write_back_from_locked_folio(mapping, wbc,
-					folio, start, end);
-			if (ret < 0) {
-				_leave(" = %zd", ret);
-				folio_batch_release(&fbatch);
-				return ret;
+			folio_put(folio);
+			if (wbc->sync_mode == WB_SYNC_NONE) {
+				if (skips >= 5 || need_resched())
+					break;
+				skips++;
 			}
+			continue;
+		}
 
-			start += ret;
+		if (!folio_clear_dirty_for_io(folio))
+			BUG();
+		ret = afs_write_back_from_locked_folio(mapping, wbc, folio, start, end);
+		folio_put(folio);
+		if (ret < 0) {
+			_leave(" = %zd", ret);
+			return ret;
 		}
 
-		folio_batch_release(&fbatch);
+		start += ret;
+
+		if (max_one_loop)
+			break;
+
 		cond_resched();
 	} while (wbc->nr_to_write > 0);
 

[PATCH 3/3] cifs: Partially revert and use filemap_get_folio_tag()

[David Howells]

Mirror the changes made to afs to partially revert the changes made by:

    acc8d8588cb7e3e64b0d2fa611dad06574cd67b1.
    "afs: convert afs_writepages_region() to use filemap_get_folios_tag()"

that were then mirrored into cifs.

The issue is that filemap_get_folios_tag() gets a batch of pages at a time,
and then cifs_writepages_region() goes through them one at a time, extends
each into an operation with as many pages as will fit using the loop in
cifs_extend_writeback() and submits it - but, in the common case, this
means that the other pages in the batch already got annexed and processed
in cifs_extend_writeback() and we end up doing duplicate processing.

Switching to write_cache_pages() isn't an immediate substitute as that
doesn't take account of PG_fscache (and this bit is used in other ways by
other filesystems).

So go back to finding the next folio from the VM one at a time and then
extending the op onwards.

Fixes: 3822a7c40997 ("Merge tag 'mm-stable-2023-02-20-13-37' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm")
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <sfrench@samba.org>
cc: Linus Torvalds <torvalds@linux-foundation.org>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: Paulo Alcantara <pc@cjr.nz>
cc: "Vishal Moola (Oracle)" <vishal.moola@gmail.com>
cc: "Matthew Wilcox (Oracle)" <willy@infradead.org>
cc: Andrew Morton <akpm@linux-foundation.org>
cc: linux-cifs@vger.kernel.org
cc: linux-mm@kvack.org
Link: https://lore.kernel.org/r/2214157.1677250083@warthog.procyon.org.uk/
---
 fs/cifs/file.c | 115 +++++++++++++++++++++----------------------------
 1 file changed, 49 insertions(+), 66 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 4d4a2d82636d..a3e89e741b42 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2864,93 +2864,76 @@ static int cifs_writepages_region(struct address_space *mapping,
 				  struct writeback_control *wbc,
 				  loff_t start, loff_t end, loff_t *_next)
 {
-	struct folio_batch fbatch;
+	struct folio *folio;
+	ssize_t ret;
 	int skips = 0;
 
-	folio_batch_init(&fbatch);
 	do {
-		int nr;
 		pgoff_t index = start / PAGE_SIZE;
 
-		nr = filemap_get_folios_tag(mapping, &index, end / PAGE_SIZE,
-					    PAGECACHE_TAG_DIRTY, &fbatch);
-		if (!nr)
+		folio = filemap_get_folio_tag(mapping, &index, end / PAGE_SIZE,
+					      PAGECACHE_TAG_DIRTY);
+		if (!folio)
 			break;
 
-		for (int i = 0; i < nr; i++) {
-			ssize_t ret;
-			struct folio *folio = fbatch.folios[i];
-
-redo_folio:
-			start = folio_pos(folio); /* May regress with THPs */
+		start = folio_pos(folio); /* May regress with THPs */
 
-			/* At this point we hold neither the i_pages lock nor the
-			 * page lock: the page may be truncated or invalidated
-			 * (changing page->mapping to NULL), or even swizzled
-			 * back from swapper_space to tmpfs file mapping
-			 */
-			if (wbc->sync_mode != WB_SYNC_NONE) {
-				ret = folio_lock_killable(folio);
-				if (ret < 0)
-					goto write_error;
-			} else {
-				if (!folio_trylock(folio))
-					goto skip_write;
+		/* At this point we hold neither the i_pages lock nor the
+		 * page lock: the page may be truncated or invalidated
+		 * (changing page->mapping to NULL), or even swizzled
+		 * back from swapper_space to tmpfs file mapping
+		 */
+		if (wbc->sync_mode != WB_SYNC_NONE) {
+			ret = folio_lock_killable(folio);
+			if (ret < 0) {
+				folio_put(folio);
+				return ret;
 			}
-
-			if (folio_mapping(folio) != mapping ||
-			    !folio_test_dirty(folio)) {
-				start += folio_size(folio);
-				folio_unlock(folio);
-				continue;
+		} else {
+			if (!folio_trylock(folio)) {
+				folio_put(folio);
+				return 0;
 			}
+		}
 
-			if (folio_test_writeback(folio) ||
-			    folio_test_fscache(folio)) {
-				folio_unlock(folio);
-				if (wbc->sync_mode == WB_SYNC_NONE)
-					goto skip_write;
+		if (folio_mapping(folio) != mapping ||
+		    !folio_test_dirty(folio)) {
+			start += folio_size(folio);
+			folio_unlock(folio);
+			folio_put(folio);
+			continue;
+		}
 
+		if (folio_test_writeback(folio) ||
+		    folio_test_fscache(folio)) {
+			folio_unlock(folio);
+			if (wbc->sync_mode != WB_SYNC_NONE) {
 				folio_wait_writeback(folio);
 #ifdef CONFIG_CIFS_FSCACHE
 				folio_wait_fscache(folio);
 #endif
-				goto redo_folio;
+			} else {
+				start += folio_size(folio);
 			}
-
-			if (!folio_clear_dirty_for_io(folio))
-				/* We hold the page lock - it should've been dirty. */
-				WARN_ON(1);
-
-			ret = cifs_write_back_from_locked_folio(mapping, wbc, folio, start, end);
-			if (ret < 0)
-				goto write_error;
-
-			start += ret;
-			continue;
-
-write_error:
-			folio_batch_release(&fbatch);
-			*_next = start;
-			return ret;
-
-skip_write:
-			/*
-			 * Too many skipped writes, or need to reschedule?
-			 * Treat it as a write error without an error code.
-			 */
-			if (skips >= 5 || need_resched()) {
-				ret = 0;
-				goto write_error;
+			folio_put(folio);
+			if (wbc->sync_mode == WB_SYNC_NONE) {
+				if (skips >= 5 || need_resched())
+					break;
+				skips++;
 			}
-
-			/* Otherwise, just skip that folio and go on to the next */
-			skips++;
-			start += folio_size(folio);
 			continue;
 		}
 
-		folio_batch_release(&fbatch);		
+		if (!folio_clear_dirty_for_io(folio))
+			/* We hold the page lock - it should've been dirty. */
+			WARN_ON(1);
+
+		ret = cifs_write_back_from_locked_folio(mapping, wbc, folio, start, end);
+		folio_put(folio);
+		if (ret < 0)
+			return ret;
+
+		start += ret;
 		cond_resched();
 	} while (wbc->nr_to_write > 0);
 

Re: [PATCH 0/3] smb3, afs: Revert changes to {cifs,afs}_writepages_region()

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> AFS firstly. ...
> 
>   Base + write_cache_pages():
> 	WRITE: bw=280MiB/s (294MB/s), 69.7MiB/s-70.5MiB/s (73.0MB/s-73.9MB/s)
> 	WRITE: bw=285MiB/s (299MB/s), 70.9MiB/s-71.5MiB/s (74.4MB/s-74.9MB/s)
> 	WRITE: bw=290MiB/s (304MB/s), 71.6MiB/s-73.2MiB/s (75.1MB/s-76.8MB/s)

Here's the patch to convert AFS to use write_cache_pages(), retaining the use
of page->private to track the dirtied part of the page.

David
---
 write.c |  382 +++++++++++++---------------------------------------------------
 1 file changed, 78 insertions(+), 304 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 571f3b9a417e..01323fa58e1c 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -14,11 +14,6 @@
 #include <linux/netfs.h>
 #include "internal.h"
 
-static int afs_writepages_region(struct address_space *mapping,
-				 struct writeback_control *wbc,
-				 loff_t start, loff_t end, loff_t *_next,
-				 bool max_one_loop);
-
 static void afs_write_to_cache(struct afs_vnode *vnode, loff_t start, size_t len,
 			       loff_t i_size, bool caching);
 
@@ -56,10 +51,8 @@ static int afs_flush_conflicting_write(struct address_space *mapping,
 		.range_start	= folio_pos(folio),
 		.range_end	= LLONG_MAX,
 	};
-	loff_t next;
 
-	return afs_writepages_region(mapping, &wbc, folio_pos(folio), LLONG_MAX,
-				     &next, true);
+	return afs_writepages(mapping, &wbc);
 }
 
 /*
@@ -449,212 +442,57 @@ static int afs_store_data(struct afs_vnode *vnode, struct iov_iter *iter, loff_t
 	return afs_put_operation(op);
 }
 
-/*
- * Extend the region to be written back to include subsequent contiguously
- * dirty pages if possible, but don't sleep while doing so.
- *
- * If this page holds new content, then we can include filler zeros in the
- * writeback.
- */
-static void afs_extend_writeback(struct address_space *mapping,
-				 struct afs_vnode *vnode,
-				 long *_count,
-				 loff_t start,
-				 loff_t max_len,
-				 bool new_content,
-				 bool caching,
-				 unsigned int *_len)
-{
-	struct pagevec pvec;
-	struct folio *folio;
-	unsigned long priv;
-	unsigned int psize, filler = 0;
-	unsigned int f, t;
-	loff_t len = *_len;
-	pgoff_t index = (start + len) / PAGE_SIZE;
-	bool stop = true;
-	unsigned int i;
-
-	XA_STATE(xas, &mapping->i_pages, index);
-	pagevec_init(&pvec);
-
-	do {
-		/* Firstly, we gather up a batch of contiguous dirty pages
-		 * under the RCU read lock - but we can't clear the dirty flags
-		 * there if any of those pages are mapped.
-		 */
-		rcu_read_lock();
-
-		xas_for_each(&xas, folio, ULONG_MAX) {
-			stop = true;
-			if (xas_retry(&xas, folio))
-				continue;
-			if (xa_is_value(folio))
-				break;
-			if (folio_index(folio) != index)
-				break;
-
-			if (!folio_try_get_rcu(folio)) {
-				xas_reset(&xas);
-				continue;
-			}
-
-			/* Has the page moved or been split? */
-			if (unlikely(folio != xas_reload(&xas))) {
-				folio_put(folio);
-				break;
-			}
-
-			if (!folio_trylock(folio)) {
-				folio_put(folio);
-				break;
-			}
-			if (!folio_test_dirty(folio) ||
-			    folio_test_writeback(folio) ||
-			    folio_test_fscache(folio)) {
-				folio_unlock(folio);
-				folio_put(folio);
-				break;
-			}
-
-			psize = folio_size(folio);
-			priv = (unsigned long)folio_get_private(folio);
-			f = afs_folio_dirty_from(folio, priv);
-			t = afs_folio_dirty_to(folio, priv);
-			if (f != 0 && !new_content) {
-				folio_unlock(folio);
-				folio_put(folio);
-				break;
-			}
-
-			len += filler + t;
-			filler = psize - t;
-			if (len >= max_len || *_count <= 0)
-				stop = true;
-			else if (t == psize || new_content)
-				stop = false;
-
-			index += folio_nr_pages(folio);
-			if (!pagevec_add(&pvec, &folio->page))
-				break;
-			if (stop)
-				break;
-		}
-
-		if (!stop)
-			xas_pause(&xas);
-		rcu_read_unlock();
-
-		/* Now, if we obtained any pages, we can shift them to being
-		 * writable and mark them for caching.
-		 */
-		if (!pagevec_count(&pvec))
-			break;
-
-		for (i = 0; i < pagevec_count(&pvec); i++) {
-			folio = page_folio(pvec.pages[i]);
-			trace_afs_folio_dirty(vnode, tracepoint_string("store+"), folio);
-
-			if (!folio_clear_dirty_for_io(folio))
-				BUG();
-			if (folio_start_writeback(folio))
-				BUG();
-			afs_folio_start_fscache(caching, folio);
-
-			*_count -= folio_nr_pages(folio);
-			folio_unlock(folio);
-		}
-
-		pagevec_release(&pvec);
-		cond_resched();
-	} while (!stop);
-
-	*_len = len;
-}
+struct afs_writepages_context {
+	unsigned long long	start;
+	unsigned long long	end;
+	unsigned long long	annex_at;
+	bool			begun;
+	bool			caching;
+	bool			new_content;
+};
 
 /*
- * Synchronously write back the locked page and any subsequent non-locked dirty
- * pages.
+ * Flush a block of pages to the server and the cache.
  */
-static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
-						struct writeback_control *wbc,
-						struct folio *folio,
-						loff_t start, loff_t end)
+static int afs_writepages_submit(struct address_space *mapping,
+				 struct writeback_control *wbc,
+				 struct afs_writepages_context *ctx)
 {
 	struct afs_vnode *vnode = AFS_FS_I(mapping->host);
 	struct iov_iter iter;
-	unsigned long priv;
-	unsigned int offset, to, len, max_len;
-	loff_t i_size = i_size_read(&vnode->netfs.inode);
-	bool new_content = test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags);
-	bool caching = fscache_cookie_enabled(afs_vnode_cache(vnode));
-	long count = wbc->nr_to_write;
+	unsigned long long i_size = i_size_read(&vnode->netfs.inode);
+	size_t len = ctx->end - ctx->start;
 	int ret;
 
-	_enter(",%lx,%llx-%llx", folio_index(folio), start, end);
-
-	if (folio_start_writeback(folio))
-		BUG();
-	afs_folio_start_fscache(caching, folio);
-
-	count -= folio_nr_pages(folio);
-
-	/* Find all consecutive lockable dirty pages that have contiguous
-	 * written regions, stopping when we find a page that is not
-	 * immediately lockable, is not dirty or is missing, or we reach the
-	 * end of the range.
-	 */
-	priv = (unsigned long)folio_get_private(folio);
-	offset = afs_folio_dirty_from(folio, priv);
-	to = afs_folio_dirty_to(folio, priv);
-	trace_afs_folio_dirty(vnode, tracepoint_string("store"), folio);
-
-	len = to - offset;
-	start += offset;
-	if (start < i_size) {
-		/* Trim the write to the EOF; the extra data is ignored.  Also
-		 * put an upper limit on the size of a single storedata op.
-		 */
-		max_len = 65536 * 4096;
-		max_len = min_t(unsigned long long, max_len, end - start + 1);
-		max_len = min_t(unsigned long long, max_len, i_size - start);
-
-		if (len < max_len &&
-		    (to == folio_size(folio) || new_content))
-			afs_extend_writeback(mapping, vnode, &count,
-					     start, max_len, new_content,
-					     caching, &len);
-		len = min_t(loff_t, len, max_len);
-	}
+	_enter("%llx-%llx", ctx->start, ctx->start + len - 1);
 
 	/* We now have a contiguous set of dirty pages, each with writeback
-	 * set; the first page is still locked at this point, but all the rest
-	 * have been unlocked.
+	 * set.
 	 */
-	folio_unlock(folio);
-
-	if (start < i_size) {
-		_debug("write back %x @%llx [%llx]", len, start, i_size);
+	if (ctx->start < i_size) {
+		if (len > i_size - ctx->start)
+			len = i_size - ctx->start;
+		_debug("write back %zx @%llx [%llx]", len, ctx->start, i_size);
 
 		/* Speculatively write to the cache.  We have to fix this up
 		 * later if the store fails.
 		 */
-		afs_write_to_cache(vnode, start, len, i_size, caching);
+		afs_write_to_cache(vnode, ctx->start, len, i_size, ctx->caching);
 
-		iov_iter_xarray(&iter, ITER_SOURCE, &mapping->i_pages, start, len);
-		ret = afs_store_data(vnode, &iter, start, false);
+		iov_iter_xarray(&iter, ITER_SOURCE,
+				&mapping->i_pages, ctx->start, len);
+		ret = afs_store_data(vnode, &iter, ctx->start, false);
 	} else {
-		_debug("write discard %x @%llx [%llx]", len, start, i_size);
+		_debug("write discard %zx @%llx [%llx]", len, ctx->start, i_size);
 
 		/* The dirty region was entirely beyond the EOF. */
-		fscache_clear_page_bits(mapping, start, len, caching);
-		afs_pages_written_back(vnode, start, len);
+		fscache_clear_page_bits(mapping, ctx->start, len, ctx->caching);
+		afs_pages_written_back(vnode, ctx->start, len);
 		ret = 0;
 	}
 
 	switch (ret) {
 	case 0:
-		wbc->nr_to_write = count;
 		ret = len;
 		break;
 
@@ -668,13 +506,13 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 	case -EKEYREJECTED:
 	case -EKEYREVOKED:
 	case -ENETRESET:
-		afs_redirty_pages(wbc, mapping, start, len);
+		afs_redirty_pages(wbc, mapping, ctx->start, len);
 		mapping_set_error(mapping, ret);
 		break;
 
 	case -EDQUOT:
 	case -ENOSPC:
-		afs_redirty_pages(wbc, mapping, start, len);
+		afs_redirty_pages(wbc, mapping, ctx->start, len);
 		mapping_set_error(mapping, -ENOSPC);
 		break;
 
@@ -686,7 +524,7 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 	case -ENOMEDIUM:
 	case -ENXIO:
 		trace_afs_file_error(vnode, ret, afs_file_error_writeback_fail);
-		afs_kill_pages(mapping, start, len);
+		afs_kill_pages(mapping, ctx->start, len);
 		mapping_set_error(mapping, ret);
 		break;
 	}
@@ -696,100 +534,51 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 }
 
 /*
- * write a region of pages back to the server
+ * Add a page to the set and flush when large enough.
  */
-static int afs_writepages_region(struct address_space *mapping,
-				 struct writeback_control *wbc,
-				 loff_t start, loff_t end, loff_t *_next,
-				 bool max_one_loop)
+static int afs_writepages_add_folio(struct folio *folio,
+				    struct writeback_control *wbc, void *data)
 {
-	struct folio *folio;
-	struct folio_batch fbatch;
-	ssize_t ret;
-	unsigned int i;
-	int n, skips = 0;
-
-	_enter("%llx,%llx,", start, end);
-	folio_batch_init(&fbatch);
-
-	do {
-		pgoff_t index = start / PAGE_SIZE;
+	struct afs_writepages_context *ctx = data;
+	struct afs_vnode *vnode = AFS_FS_I(folio->mapping->host);
+	unsigned long long pos = folio_pos(folio);
+	unsigned long priv;
+	size_t f, t;
+	int ret;
 
-		n = filemap_get_folios_tag(mapping, &index, end / PAGE_SIZE,
-					PAGECACHE_TAG_DIRTY, &fbatch);
+	priv = (unsigned long)folio_get_private(folio);
+	f = afs_folio_dirty_from(folio, priv);
+	t = afs_folio_dirty_to(folio, priv);
 
-		if (!n)
-			break;
-		for (i = 0; i < n; i++) {
-			folio = fbatch.folios[i];
-			start = folio_pos(folio); /* May regress with THPs */
-
-			_debug("wback %lx", folio_index(folio));
-
-			/* At this point we hold neither the i_pages lock nor the
-			 * page lock: the page may be truncated or invalidated
-			 * (changing page->mapping to NULL), or even swizzled
-			 * back from swapper_space to tmpfs file mapping
-			 */
-			if (wbc->sync_mode != WB_SYNC_NONE) {
-				ret = folio_lock_killable(folio);
-				if (ret < 0) {
-					folio_batch_release(&fbatch);
-					return ret;
-				}
-			} else {
-				if (!folio_trylock(folio))
-					continue;
-			}
-
-			if (folio->mapping != mapping ||
-			    !folio_test_dirty(folio)) {
-				start += folio_size(folio);
-				folio_unlock(folio);
-				continue;
-			}
-
-			if (folio_test_writeback(folio) ||
-			    folio_test_fscache(folio)) {
-				folio_unlock(folio);
-				if (wbc->sync_mode != WB_SYNC_NONE) {
-					folio_wait_writeback(folio);
-#ifdef CONFIG_AFS_FSCACHE
-					folio_wait_fscache(folio);
-#endif
-				} else {
-					start += folio_size(folio);
-				}
-				if (wbc->sync_mode == WB_SYNC_NONE) {
-					if (skips >= 5 || need_resched()) {
-						*_next = start;
-						_leave(" = 0 [%llx]", *_next);
-						return 0;
-					}
-					skips++;
-				}
-				continue;
-			}
-
-			if (!folio_clear_dirty_for_io(folio))
-				BUG();
-			ret = afs_write_back_from_locked_folio(mapping, wbc,
-					folio, start, end);
-			if (ret < 0) {
-				_leave(" = %zd", ret);
-				folio_batch_release(&fbatch);
-				return ret;
-			}
-
-			start += ret;
+	if (ctx->begun) {
+		if ((f == 0 || ctx->new_content) &&
+		    pos == ctx->annex_at) {
+			trace_afs_folio_dirty(vnode, tracepoint_string("store+"), folio);
+			goto add;
 		}
+		ret = afs_writepages_submit(folio->mapping, wbc, ctx);
+		if (ret < 0)
+			return ret;
+	}
+
+	ctx->begun	= true;
+	ctx->start	= pos + f;
+	trace_afs_folio_dirty(vnode, tracepoint_string("store"), folio);
+add:
+	ctx->end	= pos + t;
+	ctx->annex_at	= pos + folio_size(folio);
 
-		folio_batch_release(&fbatch);
-		cond_resched();
-	} while (wbc->nr_to_write > 0);
+	folio_wait_fscache(folio);
+	folio_start_writeback(folio);
+	afs_folio_start_fscache(ctx->caching, folio);
+	folio_unlock(folio);
 
-	*_next = start;
-	_leave(" = 0 [%llx]", *_next);
+	if (ctx->end - ctx->start >= 65536 * 4096) {
+		ret = afs_writepages_submit(folio->mapping, wbc, ctx);
+		if (ret < 0)
+			return ret;
+		ctx->begun = false;
+	}
 	return 0;
 }
 
@@ -800,7 +589,10 @@ int afs_writepages(struct address_space *mapping,
 		   struct writeback_control *wbc)
 {
 	struct afs_vnode *vnode = AFS_FS_I(mapping->host);
-	loff_t start, next;
+	struct afs_writepages_context ctx = {
+		.caching	= fscache_cookie_enabled(afs_vnode_cache(vnode)),
+		.new_content	= test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags),
+	};
 	int ret;
 
 	_enter("");
@@ -814,29 +606,11 @@ int afs_writepages(struct address_space *mapping,
 	else if (!down_read_trylock(&vnode->validate_lock))
 		return 0;
 
-	if (wbc->range_cyclic) {
-		start = mapping->writeback_index * PAGE_SIZE;
-		ret = afs_writepages_region(mapping, wbc, start, LLONG_MAX,
-					    &next, false);
-		if (ret == 0) {
-			mapping->writeback_index = next / PAGE_SIZE;
-			if (start > 0 && wbc->nr_to_write > 0) {
-				ret = afs_writepages_region(mapping, wbc, 0,
-							    start, &next, false);
-				if (ret == 0)
-					mapping->writeback_index =
-						next / PAGE_SIZE;
-			}
-		}
-	} else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
-		ret = afs_writepages_region(mapping, wbc, 0, LLONG_MAX,
-					    &next, false);
-		if (wbc->nr_to_write > 0 && ret == 0)
-			mapping->writeback_index = next / PAGE_SIZE;
-	} else {
-		ret = afs_writepages_region(mapping, wbc,
-					    wbc->range_start, wbc->range_end,
-					    &next, false);
+	ret = write_cache_pages(mapping, wbc, afs_writepages_add_folio, &ctx);
+	if (ret >= 0 && ctx.begun) {
+		ret = afs_writepages_submit(mapping, wbc, &ctx);
+		if (ret < 0)
+			return ret;
 	}
 
 	up_read(&vnode->validate_lock);

Re: [PATCH 1/3] mm: Add a function to get a single tagged folio from a file

[Matthew Wilcox]

On Thu, Mar 02, 2023 at 11:16:36PM +0000, David Howells wrote:
> Add a function to get a single tagged folio from a file rather than a batch
> for use in afs and cifs where, in the common case, the batch is likely to
> be rendered irrelevant by the {afs,cifs}_extend_writeback() function.

I think this is the wrong way to go.  I'll work on a replacement once
I've got a couple of other things off my plate.

Test patch to remove per-page dirty region tracking from afs

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> AFS firstly. ...
> 
>   Base + Page-dirty-region removed:
> 	WRITE: bw=301MiB/s (315MB/s), 70.4MiB/s-80.2MiB/s (73.8MB/s-84.1MB/s)
> 	WRITE: bw=325MiB/s (341MB/s), 78.5MiB/s-87.1MiB/s (82.3MB/s-91.3MB/s)
> 	WRITE: bw=320MiB/s (335MB/s), 71.6MiB/s-88.6MiB/s (75.0MB/s-92.9MB/s)

Here's a patch to remove the use of page->private data to track the dirty part
of a page from afs.

David
---
 fs/afs/file.c              |   68 ----------------
 fs/afs/internal.h          |   56 -------------
 fs/afs/write.c             |  187 +++++++++------------------------------------
 fs/cifs/file.c             |    1 
 include/trace/events/afs.h |   14 ---
 5 files changed, 45 insertions(+), 281 deletions(-)

diff --git a/fs/afs/file.c b/fs/afs/file.c
index 68d6d5dc608d..a2f3316fa174 100644
--- a/fs/afs/file.c
+++ b/fs/afs/file.c
@@ -402,80 +402,18 @@ int afs_write_inode(struct inode *inode, struct writeback_control *wbc)
 	return 0;
 }
 
-/*
- * Adjust the dirty region of the page on truncation or full invalidation,
- * getting rid of the markers altogether if the region is entirely invalidated.
- */
-static void afs_invalidate_dirty(struct folio *folio, size_t offset,
-				 size_t length)
-{
-	struct afs_vnode *vnode = AFS_FS_I(folio_inode(folio));
-	unsigned long priv;
-	unsigned int f, t, end = offset + length;
-
-	priv = (unsigned long)folio_get_private(folio);
-
-	/* we clean up only if the entire page is being invalidated */
-	if (offset == 0 && length == folio_size(folio))
-		goto full_invalidate;
-
-	 /* If the page was dirtied by page_mkwrite(), the PTE stays writable
-	  * and we don't get another notification to tell us to expand it
-	  * again.
-	  */
-	if (afs_is_folio_dirty_mmapped(priv))
-		return;
-
-	/* We may need to shorten the dirty region */
-	f = afs_folio_dirty_from(folio, priv);
-	t = afs_folio_dirty_to(folio, priv);
-
-	if (t <= offset || f >= end)
-		return; /* Doesn't overlap */
-
-	if (f < offset && t > end)
-		return; /* Splits the dirty region - just absorb it */
-
-	if (f >= offset && t <= end)
-		goto undirty;
-
-	if (f < offset)
-		t = offset;
-	else
-		f = end;
-	if (f == t)
-		goto undirty;
-
-	priv = afs_folio_dirty(folio, f, t);
-	folio_change_private(folio, (void *)priv);
-	trace_afs_folio_dirty(vnode, tracepoint_string("trunc"), folio);
-	return;
-
-undirty:
-	trace_afs_folio_dirty(vnode, tracepoint_string("undirty"), folio);
-	folio_clear_dirty_for_io(folio);
-full_invalidate:
-	trace_afs_folio_dirty(vnode, tracepoint_string("inval"), folio);
-	folio_detach_private(folio);
-}
-
 /*
  * invalidate part or all of a page
  * - release a page and clean up its private data if offset is 0 (indicating
  *   the entire page)
  */
 static void afs_invalidate_folio(struct folio *folio, size_t offset,
-			       size_t length)
+				 size_t length)
 {
-	_enter("{%lu},%zu,%zu", folio->index, offset, length);
-
-	BUG_ON(!folio_test_locked(folio));
-
-	if (folio_get_private(folio))
-		afs_invalidate_dirty(folio, offset, length);
+	struct afs_vnode *vnode = AFS_FS_I(folio_inode(folio));
 
+	trace_afs_folio_dirty(vnode, tracepoint_string("inval"), folio);
 	folio_wait_fscache(folio);
-	_leave("");
 }
 
 /*
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index ad8523d0d038..90d66b20ca8c 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -890,62 +890,6 @@ static inline void afs_invalidate_cache(struct afs_vnode *vnode, unsigned int fl
 			   i_size_read(&vnode->netfs.inode), flags);
 }
 
-/*
- * We use folio->private to hold the amount of the folio that we've written to,
- * splitting the field into two parts.  However, we need to represent a range
- * 0...FOLIO_SIZE, so we reduce the resolution if the size of the folio
- * exceeds what we can encode.
- */
-#ifdef CONFIG_64BIT
-#define __AFS_FOLIO_PRIV_MASK		0x7fffffffUL
-#define __AFS_FOLIO_PRIV_SHIFT		32
-#define __AFS_FOLIO_PRIV_MMAPPED	0x80000000UL
-#else
-#define __AFS_FOLIO_PRIV_MASK		0x7fffUL
-#define __AFS_FOLIO_PRIV_SHIFT		16
-#define __AFS_FOLIO_PRIV_MMAPPED	0x8000UL
-#endif
-
-static inline unsigned int afs_folio_dirty_resolution(struct folio *folio)
-{
-	int shift = folio_shift(folio) - (__AFS_FOLIO_PRIV_SHIFT - 1);
-	return (shift > 0) ? shift : 0;
-}
-
-static inline size_t afs_folio_dirty_from(struct folio *folio, unsigned long priv)
-{
-	unsigned long x = priv & __AFS_FOLIO_PRIV_MASK;
-
-	/* The lower bound is inclusive */
-	return x << afs_folio_dirty_resolution(folio);
-}
-
-static inline size_t afs_folio_dirty_to(struct folio *folio, unsigned long priv)
-{
-	unsigned long x = (priv >> __AFS_FOLIO_PRIV_SHIFT) & __AFS_FOLIO_PRIV_MASK;
-
-	/* The upper bound is immediately beyond the region */
-	return (x + 1) << afs_folio_dirty_resolution(folio);
-}
-
-static inline unsigned long afs_folio_dirty(struct folio *folio, size_t from, size_t to)
-{
-	unsigned int res = afs_folio_dirty_resolution(folio);
-	from >>= res;
-	to = (to - 1) >> res;
-	return (to << __AFS_FOLIO_PRIV_SHIFT) | from;
-}
-
-static inline unsigned long afs_folio_dirty_mmapped(unsigned long priv)
-{
-	return priv | __AFS_FOLIO_PRIV_MMAPPED;
-}
-
-static inline bool afs_is_folio_dirty_mmapped(unsigned long priv)
-{
-	return priv & __AFS_FOLIO_PRIV_MMAPPED;
-}
-
 #include <trace/events/afs.h>
 
 /*****************************************************************************/
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 571f3b9a417e..d2f6623c8eab 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -14,11 +14,6 @@
 #include <linux/netfs.h>
 #include "internal.h"
 
-static int afs_writepages_region(struct address_space *mapping,
-				 struct writeback_control *wbc,
-				 loff_t start, loff_t end, loff_t *_next,
-				 bool max_one_loop);
-
 static void afs_write_to_cache(struct afs_vnode *vnode, loff_t start, size_t len,
 			       loff_t i_size, bool caching);
 
@@ -43,25 +38,6 @@ static void afs_folio_start_fscache(bool caching, struct folio *folio)
 }
 #endif
 
-/*
- * Flush out a conflicting write.  This may extend the write to the surrounding
- * pages if also dirty and contiguous to the conflicting region..
- */
-static int afs_flush_conflicting_write(struct address_space *mapping,
-				       struct folio *folio)
-{
-	struct writeback_control wbc = {
-		.sync_mode	= WB_SYNC_ALL,
-		.nr_to_write	= LONG_MAX,
-		.range_start	= folio_pos(folio),
-		.range_end	= LLONG_MAX,
-	};
-	loff_t next;
-
-	return afs_writepages_region(mapping, &wbc, folio_pos(folio), LLONG_MAX,
-				     &next, true);
-}
-
 /*
  * prepare to perform part of a write to a page
  */
@@ -71,10 +47,6 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
 {
 	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
 	struct folio *folio;
-	unsigned long priv;
-	unsigned f, from;
-	unsigned t, to;
-	pgoff_t index;
 	int ret;
 
 	_enter("{%llx:%llu},%llx,%x",
@@ -88,49 +60,17 @@ int afs_write_begin(struct file *file, struct address_space *mapping,
 	if (ret < 0)
 		return ret;
 
-	index = folio_index(folio);
-	from = pos - index * PAGE_SIZE;
-	to = from + len;
-
 try_again:
-	/* See if this page is already partially written in a way that we can
-	 * merge the new write with.
-	 */
-	if (folio_test_private(folio)) {
-		priv = (unsigned long)folio_get_private(folio);
-		f = afs_folio_dirty_from(folio, priv);
-		t = afs_folio_dirty_to(folio, priv);
-		ASSERTCMP(f, <=, t);
-
-		if (folio_test_writeback(folio)) {
-			trace_afs_folio_dirty(vnode, tracepoint_string("alrdy"), folio);
-			folio_unlock(folio);
-			goto wait_for_writeback;
-		}
-		/* If the file is being filled locally, allow inter-write
-		 * spaces to be merged into writes.  If it's not, only write
-		 * back what the user gives us.
-		 */
-		if (!test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags) &&
-		    (to < f || from > t))
-			goto flush_conflicting_write;
+	if (folio_test_writeback(folio)) {
+		trace_afs_folio_dirty(vnode, tracepoint_string("alrdy"), folio);
+		folio_unlock(folio);
+		goto wait_for_writeback;
 	}
 
 	*_page = folio_file_page(folio, pos / PAGE_SIZE);
 	_leave(" = 0");
 	return 0;
 
-	/* The previous write and this write aren't adjacent or overlapping, so
-	 * flush the page out.
-	 */
-flush_conflicting_write:
-	trace_afs_folio_dirty(vnode, tracepoint_string("confl"), folio);
-	folio_unlock(folio);
-
-	ret = afs_flush_conflicting_write(mapping, folio);
-	if (ret < 0)
-		goto error;
-
 wait_for_writeback:
 	ret = folio_wait_writeback_killable(folio);
 	if (ret < 0)
@@ -156,9 +96,6 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 {
 	struct folio *folio = page_folio(subpage);
 	struct afs_vnode *vnode = AFS_FS_I(file_inode(file));
-	unsigned long priv;
-	unsigned int f, from = offset_in_folio(folio, pos);
-	unsigned int t, to = from + copied;
 	loff_t i_size, write_end_pos;
 
 	_enter("{%llx:%llu},{%lx}",
@@ -188,25 +125,10 @@ int afs_write_end(struct file *file, struct address_space *mapping,
 		fscache_update_cookie(afs_vnode_cache(vnode), NULL, &write_end_pos);
 	}
 
-	if (folio_test_private(folio)) {
-		priv = (unsigned long)folio_get_private(folio);
-		f = afs_folio_dirty_from(folio, priv);
-		t = afs_folio_dirty_to(folio, priv);
-		if (from < f)
-			f = from;
-		if (to > t)
-			t = to;
-		priv = afs_folio_dirty(folio, f, t);
-		folio_change_private(folio, (void *)priv);
-		trace_afs_folio_dirty(vnode, tracepoint_string("dirty+"), folio);
-	} else {
-		priv = afs_folio_dirty(folio, from, to);
-		folio_attach_private(folio, (void *)priv);
-		trace_afs_folio_dirty(vnode, tracepoint_string("dirty"), folio);
-	}
-
 	if (folio_mark_dirty(folio))
-		_debug("dirtied %lx", folio_index(folio));
+		trace_afs_folio_dirty(vnode, tracepoint_string("dirty"), folio);
+	else
+		trace_afs_folio_dirty(vnode, tracepoint_string("dirty+"), folio);
 
 out:
 	folio_unlock(folio);
@@ -465,18 +387,16 @@ static void afs_extend_writeback(struct address_space *mapping,
 				 bool caching,
 				 unsigned int *_len)
 {
-	struct pagevec pvec;
+	struct folio_batch batch;
 	struct folio *folio;
-	unsigned long priv;
-	unsigned int psize, filler = 0;
-	unsigned int f, t;
+	size_t psize;
 	loff_t len = *_len;
 	pgoff_t index = (start + len) / PAGE_SIZE;
 	bool stop = true;
 	unsigned int i;
-
 	XA_STATE(xas, &mapping->i_pages, index);
-	pagevec_init(&pvec);
+
+	folio_batch_init(&batch);
 
 	do {
 		/* Firstly, we gather up a batch of contiguous dirty pages
@@ -493,7 +413,6 @@ static void afs_extend_writeback(struct address_space *mapping,
 				break;
 			if (folio_index(folio) != index)
 				break;
-
 			if (!folio_try_get_rcu(folio)) {
 				xas_reset(&xas);
 				continue;
@@ -518,24 +437,13 @@ static void afs_extend_writeback(struct address_space *mapping,
 			}
 
 			psize = folio_size(folio);
-			priv = (unsigned long)folio_get_private(folio);
-			f = afs_folio_dirty_from(folio, priv);
-			t = afs_folio_dirty_to(folio, priv);
-			if (f != 0 && !new_content) {
-				folio_unlock(folio);
-				folio_put(folio);
-				break;
-			}
-
-			len += filler + t;
-			filler = psize - t;
+			len += psize;
+			stop = false;
 			if (len >= max_len || *_count <= 0)
 				stop = true;
-			else if (t == psize || new_content)
-				stop = false;
 
 			index += folio_nr_pages(folio);
-			if (!pagevec_add(&pvec, &folio->page))
+			if (!folio_batch_add(&batch, folio))
 				break;
 			if (stop)
 				break;
@@ -548,11 +456,11 @@ static void afs_extend_writeback(struct address_space *mapping,
 		/* Now, if we obtained any pages, we can shift them to being
 		 * writable and mark them for caching.
 		 */
-		if (!pagevec_count(&pvec))
+		if (!folio_batch_count(&batch))
 			break;
 
-		for (i = 0; i < pagevec_count(&pvec); i++) {
-			folio = page_folio(pvec.pages[i]);
+		for (i = 0; i < folio_batch_count(&batch); i++) {
+			folio = batch.folios[i];
 			trace_afs_folio_dirty(vnode, tracepoint_string("store+"), folio);
 
 			if (!folio_clear_dirty_for_io(folio))
@@ -565,7 +473,7 @@ static void afs_extend_writeback(struct address_space *mapping,
 			folio_unlock(folio);
 		}
 
-		pagevec_release(&pvec);
+		folio_batch_release(&batch);
 		cond_resched();
 	} while (!stop);
 
@@ -583,8 +491,7 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 {
 	struct afs_vnode *vnode = AFS_FS_I(mapping->host);
 	struct iov_iter iter;
-	unsigned long priv;
-	unsigned int offset, to, len, max_len;
+	unsigned int len, max_len;
 	loff_t i_size = i_size_read(&vnode->netfs.inode);
 	bool new_content = test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags);
 	bool caching = fscache_cookie_enabled(afs_vnode_cache(vnode));
@@ -599,18 +506,14 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 
 	count -= folio_nr_pages(folio);
 
-	/* Find all consecutive lockable dirty pages that have contiguous
-	 * written regions, stopping when we find a page that is not
-	 * immediately lockable, is not dirty or is missing, or we reach the
-	 * end of the range.
+	/* Find all consecutive lockable dirty pages, stopping when we find a
+	 * page that is not immediately lockable, is not dirty or is missing,
+	 * or we reach the end of the range.
 	 */
-	priv = (unsigned long)folio_get_private(folio);
-	offset = afs_folio_dirty_from(folio, priv);
-	to = afs_folio_dirty_to(folio, priv);
 	trace_afs_folio_dirty(vnode, tracepoint_string("store"), folio);
 
-	len = to - offset;
-	start += offset;
+	len = folio_size(folio);
+	start = folio_pos(folio);
 	if (start < i_size) {
 		/* Trim the write to the EOF; the extra data is ignored.  Also
 		 * put an upper limit on the size of a single storedata op.
@@ -619,8 +522,7 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 		max_len = min_t(unsigned long long, max_len, end - start + 1);
 		max_len = min_t(unsigned long long, max_len, i_size - start);
 
-		if (len < max_len &&
-		    (to == folio_size(folio) || new_content))
+		if (len < max_len)
 			afs_extend_writeback(mapping, vnode, &count,
 					     start, max_len, new_content,
 					     caching, &len);
@@ -909,7 +811,6 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 	struct inode *inode = file_inode(file);
 	struct afs_vnode *vnode = AFS_FS_I(inode);
 	struct afs_file *af = file->private_data;
-	unsigned long priv;
 	vm_fault_t ret = VM_FAULT_RETRY;
 
 	_enter("{{%llx:%llu}},{%lx}", vnode->fid.vid, vnode->fid.vnode, folio_index(folio));
@@ -942,15 +843,7 @@ vm_fault_t afs_page_mkwrite(struct vm_fault *vmf)
 		goto out;
 	}
 
-	priv = afs_folio_dirty(folio, 0, folio_size(folio));
-	priv = afs_folio_dirty_mmapped(priv);
-	if (folio_test_private(folio)) {
-		folio_change_private(folio, (void *)priv);
-		trace_afs_folio_dirty(vnode, tracepoint_string("mkwrite+"), folio);
-	} else {
-		folio_attach_private(folio, (void *)priv);
-		trace_afs_folio_dirty(vnode, tracepoint_string("mkwrite"), folio);
-	}
+	trace_afs_folio_dirty(vnode, tracepoint_string("mkwrite"), folio);
 	file_update_time(file);
 
 	ret = VM_FAULT_LOCKED;
@@ -992,33 +885,33 @@ void afs_prune_wb_keys(struct afs_vnode *vnode)
  */
 int afs_launder_folio(struct folio *folio)
 {
-	struct afs_vnode *vnode = AFS_FS_I(folio_inode(folio));
+	struct inode *inode = folio_inode(folio);
+	struct afs_vnode *vnode = AFS_FS_I(inode);
 	struct iov_iter iter;
 	struct bio_vec bv;
-	unsigned long priv;
-	unsigned int f, t;
 	int ret = 0;
 
 	_enter("{%lx}", folio->index);
 
-	priv = (unsigned long)folio_get_private(folio);
 	if (folio_clear_dirty_for_io(folio)) {
-		f = 0;
-		t = folio_size(folio);
-		if (folio_test_private(folio)) {
-			f = afs_folio_dirty_from(folio, priv);
-			t = afs_folio_dirty_to(folio, priv);
-		}
+		unsigned long long i_size = i_size_read(inode);
+		unsigned long long pos = folio_pos(folio);
+		size_t size = folio_size(folio);
 
-		bvec_set_folio(&bv, folio, t - f, f);
-		iov_iter_bvec(&iter, ITER_SOURCE, &bv, 1, bv.bv_len);
+		if (pos >= i_size)
+			goto out;
+		if (i_size - pos < size)
+			size = i_size - pos;
+		
+		bvec_set_folio(&bv, folio, size, 0);
+		iov_iter_bvec(&iter, ITER_SOURCE, &bv, 1, size);
 
 		trace_afs_folio_dirty(vnode, tracepoint_string("launder"), folio);
-		ret = afs_store_data(vnode, &iter, folio_pos(folio) + f, true);
+		ret = afs_store_data(vnode, &iter, pos, true);
 	}
 
+out:
 	trace_afs_folio_dirty(vnode, tracepoint_string("laundered"), folio);
-	folio_detach_private(folio);
 	folio_wait_fscache(folio);
 	return ret;
 }
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 4d4a2d82636d..3d304d4a54d6 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2674,7 +2674,6 @@ static void cifs_extend_writeback(struct address_space *mapping,
 				break;
 			}
 
-			max_pages -= nr_pages;
 			psize = folio_size(folio);
 			len += psize;
 			stop = false;
diff --git a/include/trace/events/afs.h b/include/trace/events/afs.h
index e9d412d19dbb..4540aa801edd 100644
--- a/include/trace/events/afs.h
+++ b/include/trace/events/afs.h
@@ -1025,26 +1025,16 @@ TRACE_EVENT(afs_folio_dirty,
 		    __field(struct afs_vnode *,		vnode		)
 		    __field(const char *,		where		)
 		    __field(pgoff_t,			index		)
-		    __field(unsigned long,		from		)
-		    __field(unsigned long,		to		)
 			     ),
 
 	    TP_fast_assign(
-		    unsigned long priv = (unsigned long)folio_get_private(folio);
 		    __entry->vnode = vnode;
 		    __entry->where = where;
 		    __entry->index = folio_index(folio);
-		    __entry->from  = afs_folio_dirty_from(folio, priv);
-		    __entry->to    = afs_folio_dirty_to(folio, priv);
-		    __entry->to   |= (afs_is_folio_dirty_mmapped(priv) ?
-				      (1UL << (BITS_PER_LONG - 1)) : 0);
 			   ),
 
-	    TP_printk("vn=%p %lx %s %lx-%lx%s",
-		      __entry->vnode, __entry->index, __entry->where,
-		      __entry->from,
-		      __entry->to & ~(1UL << (BITS_PER_LONG - 1)),
-		      __entry->to & (1UL << (BITS_PER_LONG - 1)) ? " M" : "")
+	    TP_printk("vn=%p %lx %s",
+		      __entry->vnode, __entry->index, __entry->where)
 	    );
 
 TRACE_EVENT(afs_call_state,

Test patch to make afs use write_cache_pages()

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> AFS firstly. ...
> 
>   Base + Page-dirty-region tracking removed +  write_cache_pages():
> 	WRITE: bw=288MiB/s (302MB/s), 71.9MiB/s-72.3MiB/s (75.4MB/s-75.8MB/s)
> 	WRITE: bw=284MiB/s (297MB/s), 70.7MiB/s-71.3MiB/s (74.1MB/s-74.8MB/s)
> 	WRITE: bw=287MiB/s (301MB/s), 71.2MiB/s-72.6MiB/s (74.7MB/s-76.1MB/s)

Here's a patch to make afs use write_cache_pages() with no per-page dirty
region tracking.  afs_extend_writeback() is removed and the folios are
accumulated via a callback function.

This goes on top of "Test patch to remove per-page dirty region tracking from
afs".

David
---
 write.c |  345 ++++++++++++----------------------------------------------------
 1 file changed, 67 insertions(+), 278 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index d2f6623c8eab..af414b72d42a 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -371,193 +371,55 @@ static int afs_store_data(struct afs_vnode *vnode, struct iov_iter *iter, loff_t
 	return afs_put_operation(op);
 }
 
-/*
- * Extend the region to be written back to include subsequent contiguously
- * dirty pages if possible, but don't sleep while doing so.
- *
- * If this page holds new content, then we can include filler zeros in the
- * writeback.
- */
-static void afs_extend_writeback(struct address_space *mapping,
-				 struct afs_vnode *vnode,
-				 long *_count,
-				 loff_t start,
-				 loff_t max_len,
-				 bool new_content,
-				 bool caching,
-				 unsigned int *_len)
-{
-	struct folio_batch batch;
-	struct folio *folio;
-	size_t psize;
-	loff_t len = *_len;
-	pgoff_t index = (start + len) / PAGE_SIZE;
-	bool stop = true;
-	unsigned int i;
-	XA_STATE(xas, &mapping->i_pages, index);
-
-	folio_batch_init(&batch);
-
-	do {
-		/* Firstly, we gather up a batch of contiguous dirty pages
-		 * under the RCU read lock - but we can't clear the dirty flags
-		 * there if any of those pages are mapped.
-		 */
-		rcu_read_lock();
-
-		xas_for_each(&xas, folio, ULONG_MAX) {
-			stop = true;
-			if (xas_retry(&xas, folio))
-				continue;
-			if (xa_is_value(folio))
-				break;
-			if (folio_index(folio) != index)
-				break;
-			if (!folio_try_get_rcu(folio)) {
-				xas_reset(&xas);
-				continue;
-			}
-
-			/* Has the page moved or been split? */
-			if (unlikely(folio != xas_reload(&xas))) {
-				folio_put(folio);
-				break;
-			}
-
-			if (!folio_trylock(folio)) {
-				folio_put(folio);
-				break;
-			}
-			if (!folio_test_dirty(folio) ||
-			    folio_test_writeback(folio) ||
-			    folio_test_fscache(folio)) {
-				folio_unlock(folio);
-				folio_put(folio);
-				break;
-			}
-
-			psize = folio_size(folio);
-			len += psize;
-			stop = false;
-			if (len >= max_len || *_count <= 0)
-				stop = true;
-
-			index += folio_nr_pages(folio);
-			if (!folio_batch_add(&batch, folio))
-				break;
-			if (stop)
-				break;
-		}
-
-		if (!stop)
-			xas_pause(&xas);
-		rcu_read_unlock();
-
-		/* Now, if we obtained any pages, we can shift them to being
-		 * writable and mark them for caching.
-		 */
-		if (!folio_batch_count(&batch))
-			break;
-
-		for (i = 0; i < folio_batch_count(&batch); i++) {
-			folio = batch.folios[i];
-			trace_afs_folio_dirty(vnode, tracepoint_string("store+"), folio);
-
-			if (!folio_clear_dirty_for_io(folio))
-				BUG();
-			if (folio_start_writeback(folio))
-				BUG();
-			afs_folio_start_fscache(caching, folio);
-
-			*_count -= folio_nr_pages(folio);
-			folio_unlock(folio);
-		}
-
-		folio_batch_release(&batch);
-		cond_resched();
-	} while (!stop);
-
-	*_len = len;
-}
+struct afs_writepages_context {
+	unsigned long long	start;
+	size_t			len;
+	bool			begun;
+	bool			caching;
+};
 
 /*
- * Synchronously write back the locked page and any subsequent non-locked dirty
- * pages.
+ * Flush a block of pages to the server and the cache.
  */
-static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
-						struct writeback_control *wbc,
-						struct folio *folio,
-						loff_t start, loff_t end)
+static int afs_writepages_submit(struct address_space *mapping,
+				 struct writeback_control *wbc,
+				 struct afs_writepages_context *ctx)
 {
 	struct afs_vnode *vnode = AFS_FS_I(mapping->host);
 	struct iov_iter iter;
-	unsigned int len, max_len;
-	loff_t i_size = i_size_read(&vnode->netfs.inode);
-	bool new_content = test_bit(AFS_VNODE_NEW_CONTENT, &vnode->flags);
-	bool caching = fscache_cookie_enabled(afs_vnode_cache(vnode));
-	long count = wbc->nr_to_write;
+	unsigned long long i_size = i_size_read(&vnode->netfs.inode);
 	int ret;
 
-	_enter(",%lx,%llx-%llx", folio_index(folio), start, end);
-
-	if (folio_start_writeback(folio))
-		BUG();
-	afs_folio_start_fscache(caching, folio);
-
-	count -= folio_nr_pages(folio);
-
-	/* Find all consecutive lockable dirty pages, stopping when we find a
-	 * page that is not immediately lockable, is not dirty or is missing,
-	 * or we reach the end of the range.
-	 */
-	trace_afs_folio_dirty(vnode, tracepoint_string("store"), folio);
-
-	len = folio_size(folio);
-	start = folio_pos(folio);
-	if (start < i_size) {
-		/* Trim the write to the EOF; the extra data is ignored.  Also
-		 * put an upper limit on the size of a single storedata op.
-		 */
-		max_len = 65536 * 4096;
-		max_len = min_t(unsigned long long, max_len, end - start + 1);
-		max_len = min_t(unsigned long long, max_len, i_size - start);
-
-		if (len < max_len)
-			afs_extend_writeback(mapping, vnode, &count,
-					     start, max_len, new_content,
-					     caching, &len);
-		len = min_t(loff_t, len, max_len);
-	}
+	_enter("%llx-%llx", ctx->start, ctx->start + ctx->len - 1);
 
 	/* We now have a contiguous set of dirty pages, each with writeback
-	 * set; the first page is still locked at this point, but all the rest
-	 * have been unlocked.
+	 * set.
 	 */
-	folio_unlock(folio);
-
-	if (start < i_size) {
-		_debug("write back %x @%llx [%llx]", len, start, i_size);
+	if (ctx->start < i_size) {
+		if (ctx->len > i_size - ctx->start)
+			ctx->len = i_size - ctx->start;
+		_debug("write back %zx @%llx [%llx]", ctx->len, ctx->start, i_size);
 
 		/* Speculatively write to the cache.  We have to fix this up
 		 * later if the store fails.
 		 */
-		afs_write_to_cache(vnode, start, len, i_size, caching);
+		afs_write_to_cache(vnode, ctx->start, ctx->len, i_size, ctx->caching);
 
-		iov_iter_xarray(&iter, ITER_SOURCE, &mapping->i_pages, start, len);
-		ret = afs_store_data(vnode, &iter, start, false);
+		iov_iter_xarray(&iter, ITER_SOURCE,
+				&mapping->i_pages, ctx->start, ctx->len);
+		ret = afs_store_data(vnode, &iter, ctx->start, false);
 	} else {
-		_debug("write discard %x @%llx [%llx]", len, start, i_size);
+		_debug("write discard %zx @%llx [%llx]", ctx->len, ctx->start, i_size);
 
 		/* The dirty region was entirely beyond the EOF. */
-		fscache_clear_page_bits(mapping, start, len, caching);
-		afs_pages_written_back(vnode, start, len);
+		fscache_clear_page_bits(mapping, ctx->start, ctx->len, ctx->caching);
+		afs_pages_written_back(vnode, ctx->start, ctx->len);
 		ret = 0;
 	}
 
 	switch (ret) {
 	case 0:
-		wbc->nr_to_write = count;
-		ret = len;
+		ret = ctx->len;
 		break;
 
 	default:
@@ -570,13 +432,13 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 	case -EKEYREJECTED:
 	case -EKEYREVOKED:
 	case -ENETRESET:
-		afs_redirty_pages(wbc, mapping, start, len);
+		afs_redirty_pages(wbc, mapping, ctx->start, ctx->len);
 		mapping_set_error(mapping, ret);
 		break;
 
 	case -EDQUOT:
 	case -ENOSPC:
-		afs_redirty_pages(wbc, mapping, start, len);
+		afs_redirty_pages(wbc, mapping, ctx->start, ctx->len);
 		mapping_set_error(mapping, -ENOSPC);
 		break;
 
@@ -588,7 +450,7 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 	case -ENOMEDIUM:
 	case -ENXIO:
 		trace_afs_file_error(vnode, ret, afs_file_error_writeback_fail);
-		afs_kill_pages(mapping, start, len);
+		afs_kill_pages(mapping, ctx->start, ctx->len);
 		mapping_set_error(mapping, ret);
 		break;
 	}
@@ -598,100 +460,43 @@ static ssize_t afs_write_back_from_locked_folio(struct address_space *mapping,
 }
 
 /*
- * write a region of pages back to the server
+ * Add a page to the set and flush when large enough.
  */
-static int afs_writepages_region(struct address_space *mapping,
-				 struct writeback_control *wbc,
-				 loff_t start, loff_t end, loff_t *_next,
-				 bool max_one_loop)
+static int afs_writepages_add_folio(struct folio *folio,
+				    struct writeback_control *wbc, void *data)
 {
-	struct folio *folio;
-	struct folio_batch fbatch;
-	ssize_t ret;
-	unsigned int i;
-	int n, skips = 0;
-
-	_enter("%llx,%llx,", start, end);
-	folio_batch_init(&fbatch);
-
-	do {
-		pgoff_t index = start / PAGE_SIZE;
-
-		n = filemap_get_folios_tag(mapping, &index, end / PAGE_SIZE,
-					PAGECACHE_TAG_DIRTY, &fbatch);
+	struct afs_writepages_context *ctx = data;
+	struct afs_vnode *vnode = AFS_FS_I(folio->mapping->host);
+	int ret;
 
-		if (!n)
-			break;
-		for (i = 0; i < n; i++) {
-			folio = fbatch.folios[i];
-			start = folio_pos(folio); /* May regress with THPs */
-
-			_debug("wback %lx", folio_index(folio));
-
-			/* At this point we hold neither the i_pages lock nor the
-			 * page lock: the page may be truncated or invalidated
-			 * (changing page->mapping to NULL), or even swizzled
-			 * back from swapper_space to tmpfs file mapping
-			 */
-			if (wbc->sync_mode != WB_SYNC_NONE) {
-				ret = folio_lock_killable(folio);
-				if (ret < 0) {
-					folio_batch_release(&fbatch);
-					return ret;
-				}
-			} else {
-				if (!folio_trylock(folio))
-					continue;
-			}
-
-			if (folio->mapping != mapping ||
-			    !folio_test_dirty(folio)) {
-				start += folio_size(folio);
-				folio_unlock(folio);
-				continue;
-			}
-
-			if (folio_test_writeback(folio) ||
-			    folio_test_fscache(folio)) {
-				folio_unlock(folio);
-				if (wbc->sync_mode != WB_SYNC_NONE) {
-					folio_wait_writeback(folio);
-#ifdef CONFIG_AFS_FSCACHE
-					folio_wait_fscache(folio);
-#endif
-				} else {
-					start += folio_size(folio);
-				}
-				if (wbc->sync_mode == WB_SYNC_NONE) {
-					if (skips >= 5 || need_resched()) {
-						*_next = start;
-						_leave(" = 0 [%llx]", *_next);
-						return 0;
-					}
-					skips++;
-				}
-				continue;
-			}
-
-			if (!folio_clear_dirty_for_io(folio))
-				BUG();
-			ret = afs_write_back_from_locked_folio(mapping, wbc,
-					folio, start, end);
-			if (ret < 0) {
-				_leave(" = %zd", ret);
-				folio_batch_release(&fbatch);
-				return ret;
-			}
-
-			start += ret;
+	if (ctx->begun) {
+		if (folio_pos(folio) == ctx->start + ctx->len) {
+			trace_afs_folio_dirty(vnode, tracepoint_string("store+"), folio);
+			goto add;
 		}
+		ret = afs_writepages_submit(folio->mapping, wbc, ctx);
+		if (ret < 0)
+			return ret;
+	}
 
-		folio_batch_release(&fbatch);
-		cond_resched();
-	} while (wbc->nr_to_write > 0);
+	ctx->begun = true;
+	ctx->start = folio_pos(folio);
+	ctx->len = 0;
+	trace_afs_folio_dirty(vnode, tracepoint_string("store"), folio);
+add:
+	ctx->len += folio_size(folio);
 
-	*_next = start;
-	_leave(" = 0 [%llx]", *_next);
+	folio_wait_fscache(folio);
+	folio_start_writeback(folio);
+	afs_folio_start_fscache(ctx->caching, folio);
+	folio_unlock(folio);
+
+	if (ctx->len >= 65536 * 4096) {
+		ret = afs_writepages_submit(folio->mapping, wbc, ctx);
+		if (ret < 0)
+			return ret;
+		ctx->begun = false;
+	}
 	return 0;
 }
 
@@ -702,7 +507,9 @@ int afs_writepages(struct address_space *mapping,
 		   struct writeback_control *wbc)
 {
 	struct afs_vnode *vnode = AFS_FS_I(mapping->host);
-	loff_t start, next;
+	struct afs_writepages_context ctx = {
+		.caching = fscache_cookie_enabled(afs_vnode_cache(vnode)),
+	};
 	int ret;
 
 	_enter("");
@@ -716,29 +523,11 @@ int afs_writepages(struct address_space *mapping,
 	else if (!down_read_trylock(&vnode->validate_lock))
 		return 0;
 
-	if (wbc->range_cyclic) {
-		start = mapping->writeback_index * PAGE_SIZE;
-		ret = afs_writepages_region(mapping, wbc, start, LLONG_MAX,
-					    &next, false);
-		if (ret == 0) {
-			mapping->writeback_index = next / PAGE_SIZE;
-			if (start > 0 && wbc->nr_to_write > 0) {
-				ret = afs_writepages_region(mapping, wbc, 0,
-							    start, &next, false);
-				if (ret == 0)
-					mapping->writeback_index =
-						next / PAGE_SIZE;
-			}
-		}
-	} else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
-		ret = afs_writepages_region(mapping, wbc, 0, LLONG_MAX,
-					    &next, false);
-		if (wbc->nr_to_write > 0 && ret == 0)
-			mapping->writeback_index = next / PAGE_SIZE;
-	} else {
-		ret = afs_writepages_region(mapping, wbc,
-					    wbc->range_start, wbc->range_end,
-					    &next, false);
+	ret = write_cache_pages(mapping, wbc, afs_writepages_add_folio, &ctx);
+	if (ret >= 0 && ctx.begun) {
+		ret = afs_writepages_submit(mapping, wbc, &ctx);
+		if (ret < 0)
+			return ret;
 	}
 
 	up_read(&vnode->validate_lock);

Test patch to make afs use its own version of write_cache_pages()

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> AFS firstly. ...
> 
>   Base + Page-dirty-region tracking removed + Own write_cache_pages()
> 	WRITE: bw=302MiB/s (316MB/s), 75.1MiB/s-76.1MiB/s (78.7MB/s-79.8MB/s)
> 	WRITE: bw=302MiB/s (316MB/s), 74.5MiB/s-76.1MiB/s (78.1MB/s-79.8MB/s)
> 	WRITE: bw=301MiB/s (316MB/s), 75.2MiB/s-75.5MiB/s (78.9MB/s-79.1MB/s)


This goes on top of "Test patch to remove per-page dirty region tracking from
afs" and "Test patch to make afs use write_cache_pages()"

David
---
 write.c |  141 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 138 insertions(+), 3 deletions(-)

diff --git a/fs/afs/write.c b/fs/afs/write.c
index 86b6e7cbe17c..d66c05acda8c 100644
--- a/fs/afs/write.c
+++ b/fs/afs/write.c
@@ -463,9 +463,9 @@ static int afs_writepages_submit(struct address_space *mapping,
  * Add a page to the set and flush when large enough.
  */
 static int afs_writepages_add_folio(struct folio *folio,
-				    struct writeback_control *wbc, void *data)
+				    struct writeback_control *wbc,
+				    struct afs_writepages_context *ctx)
 {
-	struct afs_writepages_context *ctx = data;
 	struct afs_vnode *vnode = AFS_FS_I(folio->mapping->host);
 	int ret;
 
@@ -499,6 +499,141 @@ static int afs_writepages_add_folio(struct folio *folio,
 	}
 	return 0;
 }
+static int afs_write_cache_pages(struct address_space *mapping,
+				 struct writeback_control *wbc,
+				 struct afs_writepages_context *ctx)
+{
+	int ret = 0;
+	int done = 0;
+	int error;
+	struct folio_batch fbatch;
+	int nr_folios;
+	pgoff_t index;
+	pgoff_t end;		/* Inclusive */
+	pgoff_t done_index;
+	int range_whole = 0;
+	xa_mark_t tag;
+
+	folio_batch_init(&fbatch);
+	if (wbc->range_cyclic) {
+		index = mapping->writeback_index; /* prev offset */
+		end = -1;
+	} else {
+		index = wbc->range_start >> PAGE_SHIFT;
+		end = wbc->range_end >> PAGE_SHIFT;
+		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
+			range_whole = 1;
+	}
+	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
+		tag_pages_for_writeback(mapping, index, end);
+		tag = PAGECACHE_TAG_TOWRITE;
+	} else {
+		tag = PAGECACHE_TAG_DIRTY;
+	}
+	done_index = index;
+	while (!done && (index <= end)) {
+		int i;
+
+		nr_folios = filemap_get_folios_tag(mapping, &index, end,
+				tag, &fbatch);
+
+		if (nr_folios == 0)
+			break;
+
+		for (i = 0; i < nr_folios; i++) {
+			struct folio *folio = fbatch.folios[i];
+
+			done_index = folio->index;
+
+			folio_lock(folio);
+
+			/*
+			 * Page truncated or invalidated. We can freely skip it
+			 * then, even for data integrity operations: the page
+			 * has disappeared concurrently, so there could be no
+			 * real expectation of this data integrity operation
+			 * even if there is now a new, dirty page at the same
+			 * pagecache address.
+			 */
+			if (unlikely(folio->mapping != mapping)) {
+continue_unlock:
+				folio_unlock(folio);
+				continue;
+			}
+
+			if (!folio_test_dirty(folio)) {
+				/* someone wrote it for us */
+				goto continue_unlock;
+			}
+
+			if (folio_test_writeback(folio)) {
+				if (wbc->sync_mode != WB_SYNC_NONE)
+					folio_wait_writeback(folio);
+				else
+					goto continue_unlock;
+			}
+
+			BUG_ON(folio_test_writeback(folio));
+			if (!folio_clear_dirty_for_io(folio))
+				goto continue_unlock;
+
+			//trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
+			error = afs_writepages_add_folio(folio, wbc, ctx);
+			if (unlikely(error)) {
+				/*
+				 * Handle errors according to the type of
+				 * writeback. There's no need to continue for
+				 * background writeback. Just push done_index
+				 * past this page so media errors won't choke
+				 * writeout for the entire file. For integrity
+				 * writeback, we must process the entire dirty
+				 * set regardless of errors because the fs may
+				 * still have state to clear for each page. In
+				 * that case we continue processing and return
+				 * the first error.
+				 */
+				if (error == AOP_WRITEPAGE_ACTIVATE) {
+					folio_unlock(folio);
+					error = 0;
+				} else if (wbc->sync_mode != WB_SYNC_ALL) {
+					ret = error;
+					done_index = folio->index +
+						folio_nr_pages(folio);
+					done = 1;
+					break;
+				}
+				if (!ret)
+					ret = error;
+			}
+
+			/*
+			 * We stop writing back only if we are not doing
+			 * integrity sync. In case of integrity sync we have to
+			 * keep going until we have written all the pages
+			 * we tagged for writeback prior to entering this loop.
+			 */
+			if (--wbc->nr_to_write <= 0 &&
+			    wbc->sync_mode == WB_SYNC_NONE) {
+				done = 1;
+				break;
+			}
+		}
+		folio_batch_release(&fbatch);
+		cond_resched();
+	}
+
+	/*
+	 * If we hit the last page and there is more work to be done: wrap
+	 * back the index back to the start of the file for the next
+	 * time we are called.
+	 */
+	if (wbc->range_cyclic && !done)
+		done_index = 0;
+	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
+		mapping->writeback_index = done_index;
+
+	return ret;
+}
 
 /*
  * write some of the pending data back to the server
@@ -523,7 +658,7 @@ int afs_writepages(struct address_space *mapping,
 	else if (!down_read_trylock(&vnode->validate_lock))
 		return 0;
 
-	ret = write_cache_pages(mapping, wbc, afs_writepages_add_folio, &ctx);
+	ret = afs_write_cache_pages(mapping, wbc, &ctx);
 	if (ret >= 0 && ctx.begun)
 		ret = afs_writepages_submit(mapping, wbc, &ctx);
 

cifs test patch to convert to using write_cache_pages()

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> And then CIFS. ...
> 
>   Base + write_cache_pages():
> 	WRITE: bw=457MiB/s (479MB/s), 114MiB/s-114MiB/s (120MB/s-120MB/s)
> 	WRITE: bw=449MiB/s (471MB/s), 112MiB/s-113MiB/s (118MB/s-118MB/s)
> 	WRITE: bw=459MiB/s (482MB/s), 115MiB/s-115MiB/s (120MB/s-121MB/s)

Here's my patch to convert cifs to use write_cache_pages().

David
---
 fs/cifs/file.c |  400 ++++++++++++++++-----------------------------------------
 1 file changed, 115 insertions(+), 285 deletions(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 3d304d4a54d6..04e2466609d9 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2613,140 +2613,35 @@ static int cifs_partialpagewrite(struct page *page, unsigned from, unsigned to)
 	return rc;
 }
 
-/*
- * Extend the region to be written back to include subsequent contiguously
- * dirty pages if possible, but don't sleep while doing so.
- */
-static void cifs_extend_writeback(struct address_space *mapping,
-				  long *_count,
-				  loff_t start,
-				  int max_pages,
-				  size_t max_len,
-				  unsigned int *_len)
-{
-	struct folio_batch batch;
-	struct folio *folio;
-	unsigned int psize, nr_pages;
-	size_t len = *_len;
-	pgoff_t index = (start + len) / PAGE_SIZE;
-	bool stop = true;
-	unsigned int i;
-	XA_STATE(xas, &mapping->i_pages, index);
-
-	folio_batch_init(&batch);
-
-	do {
-		/* Firstly, we gather up a batch of contiguous dirty pages
-		 * under the RCU read lock - but we can't clear the dirty flags
-		 * there if any of those pages are mapped.
-		 */
-		rcu_read_lock();
-
-		xas_for_each(&xas, folio, ULONG_MAX) {
-			stop = true;
-			if (xas_retry(&xas, folio))
-				continue;
-			if (xa_is_value(folio))
-				break;
-			if (folio_index(folio) != index)
-				break;
-			if (!folio_try_get_rcu(folio)) {
-				xas_reset(&xas);
-				continue;
-			}
-			nr_pages = folio_nr_pages(folio);
-			if (nr_pages > max_pages)
-				break;
-
-			/* Has the page moved or been split? */
-			if (unlikely(folio != xas_reload(&xas))) {
-				folio_put(folio);
-				break;
-			}
-
-			if (!folio_trylock(folio)) {
-				folio_put(folio);
-				break;
-			}
-			if (!folio_test_dirty(folio) || folio_test_writeback(folio)) {
-				folio_unlock(folio);
-				folio_put(folio);
-				break;
-			}
-
-			psize = folio_size(folio);
-			len += psize;
-			stop = false;
-			if (max_pages <= 0 || len >= max_len || *_count <= 0)
-				stop = true;
-
-			index += nr_pages;
-			if (!folio_batch_add(&batch, folio))
-				break;
-			if (stop)
-				break;
-		}
-
-		if (!stop)
-			xas_pause(&xas);
-		rcu_read_unlock();
-
-		/* Now, if we obtained any pages, we can shift them to being
-		 * writable and mark them for caching.
-		 */
-		if (!folio_batch_count(&batch))
-			break;
-
-		for (i = 0; i < folio_batch_count(&batch); i++) {
-			folio = batch.folios[i];
-			/* The folio should be locked, dirty and not undergoing
-			 * writeback from the loop above.
-			 */
-			if (!folio_clear_dirty_for_io(folio))
-				WARN_ON(1);
-			if (folio_start_writeback(folio))
-				WARN_ON(1);
-
-			*_count -= folio_nr_pages(folio);
-			folio_unlock(folio);
-		}
-
-		folio_batch_release(&batch);
-		cond_resched();
-	} while (!stop);
-
-	*_len = len;
-}
+struct cifs_writepages_context {
+	struct cifs_writedata	*wdata;
+	struct TCP_Server_Info	*server;
+	struct cifs_credits	credits;
+	unsigned long long	start;
+	size_t			len;
+	size_t			wsize;
+	unsigned int		xid;
+	bool			begun;
+	bool			caching;
+};
 
 /*
- * Write back the locked page and any subsequent non-locked dirty pages.
+ * Set up a writeback op.
  */
-static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
-						 struct writeback_control *wbc,
-						 struct folio *folio,
-						 loff_t start, loff_t end)
+static int cifs_writeback_begin(struct address_space *mapping,
+				struct writeback_control *wbc,
+				unsigned long long start,
+				struct cifs_writepages_context *ctx)
 {
 	struct inode *inode = mapping->host;
 	struct TCP_Server_Info *server;
 	struct cifs_writedata *wdata;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(inode->i_sb);
-	struct cifs_credits credits_on_stack;
-	struct cifs_credits *credits = &credits_on_stack;
 	struct cifsFileInfo *cfile = NULL;
-	unsigned int xid, wsize, len;
-	loff_t i_size = i_size_read(inode);
-	size_t max_len;
-	long count = wbc->nr_to_write;
+	unsigned int wsize, len;
 	int rc;
 
-	/* The folio should be locked, dirty and not undergoing writeback. */
-	if (folio_start_writeback(folio))
-		WARN_ON(1);
-
-	count -= folio_nr_pages(folio);
-	len = folio_size(folio);
-
-	xid = get_xid();
+	ctx->xid = get_xid();
 	server = cifs_pick_channel(cifs_sb_master_tcon(cifs_sb)->ses);
 
 	rc = cifs_get_writable_file(CIFS_I(inode), FIND_WR_ANY, &cfile);
@@ -2756,7 +2651,7 @@ static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
 	}
 
 	rc = server->ops->wait_mtu_credits(server, cifs_sb->ctx->wsize,
-					   &wsize, credits);
+					   &wsize, &ctx->credits);
 	if (rc != 0)
 		goto err_close;
 
@@ -2767,56 +2662,60 @@ static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
 	}
 
 	wdata->sync_mode = wbc->sync_mode;
-	wdata->offset = folio_pos(folio);
+	wdata->offset = start;
 	wdata->pid = cfile->pid;
-	wdata->credits = credits_on_stack;
+	wdata->credits = ctx->credits;
 	wdata->cfile = cfile;
 	wdata->server = server;
-	cfile = NULL;
-
-	/* Find all consecutive lockable dirty pages, stopping when we find a
-	 * page that is not immediately lockable, is not dirty or is missing,
-	 * or we reach the end of the range.
-	 */
-	if (start < i_size) {
-		/* Trim the write to the EOF; the extra data is ignored.  Also
-		 * put an upper limit on the size of a single storedata op.
-		 */
-		max_len = wsize;
-		max_len = min_t(unsigned long long, max_len, end - start + 1);
-		max_len = min_t(unsigned long long, max_len, i_size - start);
-
-		if (len < max_len) {
-			int max_pages = INT_MAX;
-
-#ifdef CONFIG_CIFS_SMB_DIRECT
-			if (server->smbd_conn)
-				max_pages = server->smbd_conn->max_frmr_depth;
-#endif
-			max_pages -= folio_nr_pages(folio);
+	ctx->wsize = wsize;
+	ctx->server = server;
+	ctx->wdata = wdata;
+	ctx->begun = true;
+	return 0;
 
-			if (max_pages > 0)
-				cifs_extend_writeback(mapping, &count, start,
-						      max_pages, max_len, &len);
-		}
-		len = min_t(loff_t, len, max_len);
+err_uncredit:
+	add_credits_and_wake_if(server, &ctx->credits, 0);
+err_close:
+	if (cfile)
+		cifsFileInfo_put(cfile);
+err_xid:
+	free_xid(ctx->xid);
+	if (is_retryable_error(rc)) {
+		cifs_pages_write_redirty(inode, start, len);
+	} else {
+		cifs_pages_write_failed(inode, start, len);
+		mapping_set_error(mapping, rc);
 	}
+	/* Indication to update ctime and mtime as close is deferred */
+	set_bit(CIFS_INO_MODIFIED_ATTR, &CIFS_I(inode)->flags);
+	return rc;
+}
 
-	wdata->bytes = len;
+/*
+ * Flush a block of pages to the server and the cache.
+ */
+static int cifs_writepages_submit(struct address_space *mapping,
+				  struct writeback_control *wbc,
+				  struct cifs_writepages_context *ctx)
+{
+	struct TCP_Server_Info *server = ctx->server;
+	struct cifs_writedata *wdata = ctx->wdata;
+	unsigned long long i_size = i_size_read(mapping->host);
+	int rc;
 
-	/* We now have a contiguous set of dirty pages, each with writeback
-	 * set; the first page is still locked at this point, but all the rest
-	 * have been unlocked.
+	/* We now have a contiguous set of dirty pages, each with
+	 * writeback set.
 	 */
-	folio_unlock(folio);
-
-	if (start < i_size) {
-		iov_iter_xarray(&wdata->iter, ITER_SOURCE, &mapping->i_pages,
-				start, len);
+	if (ctx->start < i_size) {
+		if (ctx->len > i_size - ctx->start)
+			ctx->len = i_size - ctx->start;
+		wdata->bytes = ctx->len;
+		iov_iter_xarray(&wdata->iter, ITER_SOURCE,
+				&mapping->i_pages, ctx->start, wdata->bytes);
 
 		rc = adjust_credits(wdata->server, &wdata->credits, wdata->bytes);
 		if (rc)
-			goto err_wdata;
+			goto err;
 
 		if (wdata->cfile->invalidHandle)
 			rc = -EAGAIN;
@@ -2827,133 +2726,79 @@ static ssize_t cifs_write_back_from_locked_folio(struct address_space *mapping,
 			kref_put(&wdata->refcount, cifs_writedata_release);
 			goto err_close;
 		}
+
 	} else {
 		/* The dirty region was entirely beyond the EOF. */
-		cifs_pages_written_back(inode, start, len);
+		cifs_pages_written_back(mapping->host, ctx->start, ctx->len);
 		rc = 0;
 	}
 
-err_wdata:
+err:
 	kref_put(&wdata->refcount, cifs_writedata_release);
-err_uncredit:
-	add_credits_and_wake_if(server, credits, 0);
+	add_credits_and_wake_if(server, &ctx->credits, 0);
 err_close:
-	if (cfile)
-		cifsFileInfo_put(cfile);
-err_xid:
-	free_xid(xid);
+	free_xid(ctx->xid);
 	if (rc == 0) {
-		wbc->nr_to_write = count;
-		rc = len;
+		rc = 0;
 	} else if (is_retryable_error(rc)) {
-		cifs_pages_write_redirty(inode, start, len);
+		cifs_pages_write_redirty(mapping->host, ctx->start, ctx->len);
 	} else {
-		cifs_pages_write_failed(inode, start, len);
+		cifs_pages_write_failed(mapping->host, ctx->start, ctx->len);
 		mapping_set_error(mapping, rc);
 	}
+
 	/* Indication to update ctime and mtime as close is deferred */
-	set_bit(CIFS_INO_MODIFIED_ATTR, &CIFS_I(inode)->flags);
+	set_bit(CIFS_INO_MODIFIED_ATTR, &CIFS_I(mapping->host)->flags);
+	ctx->wdata = NULL;
+	ctx->begun = false;
 	return rc;
 }
 
 /*
- * write a region of pages back to the server
+ * Add a page to the set and flush when large enough.
  */
-static int cifs_writepages_region(struct address_space *mapping,
-				  struct writeback_control *wbc,
-				  loff_t start, loff_t end, loff_t *_next)
+static int cifs_writepages_add_folio(struct folio *folio,
+				     struct writeback_control *wbc, void *data)
 {
-	struct folio_batch fbatch;
-	int skips = 0;
-
-	folio_batch_init(&fbatch);
-	do {
-		int nr;
-		pgoff_t index = start / PAGE_SIZE;
-
-		nr = filemap_get_folios_tag(mapping, &index, end / PAGE_SIZE,
-					    PAGECACHE_TAG_DIRTY, &fbatch);
-		if (!nr)
-			break;
-
-		for (int i = 0; i < nr; i++) {
-			ssize_t ret;
-			struct folio *folio = fbatch.folios[i];
-
-redo_folio:
-			start = folio_pos(folio); /* May regress with THPs */
-
-			/* At this point we hold neither the i_pages lock nor the
-			 * page lock: the page may be truncated or invalidated
-			 * (changing page->mapping to NULL), or even swizzled
-			 * back from swapper_space to tmpfs file mapping
-			 */
-			if (wbc->sync_mode != WB_SYNC_NONE) {
-				ret = folio_lock_killable(folio);
-				if (ret < 0)
-					goto write_error;
-			} else {
-				if (!folio_trylock(folio))
-					goto skip_write;
-			}
-
-			if (folio_mapping(folio) != mapping ||
-			    !folio_test_dirty(folio)) {
-				start += folio_size(folio);
-				folio_unlock(folio);
-				continue;
-			}
-
-			if (folio_test_writeback(folio) ||
-			    folio_test_fscache(folio)) {
-				folio_unlock(folio);
-				if (wbc->sync_mode == WB_SYNC_NONE)
-					goto skip_write;
-
-				folio_wait_writeback(folio);
-#ifdef CONFIG_CIFS_FSCACHE
-				folio_wait_fscache(folio);
-#endif
-				goto redo_folio;
-			}
-
-			if (!folio_clear_dirty_for_io(folio))
-				/* We hold the page lock - it should've been dirty. */
-				WARN_ON(1);
+	struct cifs_writepages_context *ctx = data;
+	unsigned long long i_size = i_size_read(folio->mapping->host);
+	unsigned long long pos = folio_pos(folio);
+	size_t size = folio_size(folio);
+	int ret;
 
-			ret = cifs_write_back_from_locked_folio(mapping, wbc, folio, start, end);
-			if (ret < 0)
-				goto write_error;
+	if (pos < i_size && size > i_size - pos)
+		size = i_size - pos;
 
-			start += ret;
-			continue;
-
-write_error:
-			folio_batch_release(&fbatch);
-			*_next = start;
+	if (ctx->begun) {
+		if (pos == ctx->start + ctx->len &&
+		    ctx->len + size <= ctx->wsize)
+			goto add;
+		ret = cifs_writepages_submit(folio->mapping, wbc, ctx);
+		if (ret < 0) {
+			ctx->begun = false;
 			return ret;
+		}
+	}
 
-skip_write:
-			/*
-			 * Too many skipped writes, or need to reschedule?
-			 * Treat it as a write error without an error code.
-			 */
-			if (skips >= 5 || need_resched()) {
-				ret = 0;
-				goto write_error;
-			}
+	ret = cifs_writeback_begin(folio->mapping, wbc, pos, ctx);
+	if (ret < 0)
+		return ret;
 
-			/* Otherwise, just skip that folio and go on to the next */
-			skips++;
-			start += folio_size(folio);
-			continue;
-		}
+	ctx->start = folio_pos(folio);
+	ctx->len = 0;
+add:
+	ctx->len += folio_size(folio);
 
-		folio_batch_release(&fbatch);		
-		cond_resched();
-	} while (wbc->nr_to_write > 0);
+	folio_wait_fscache(folio);
+	folio_start_writeback(folio);
+	folio_unlock(folio);
 
-	*_next = start;
+	if (ctx->len >= ctx->wsize) {
+		ret = cifs_writepages_submit(folio->mapping, wbc, ctx);
+		if (ret < 0)
+			return ret;
+		ctx->begun = false;
+	}
 	return 0;
 }
 
@@ -2963,7 +2808,7 @@ static int cifs_writepages_region(struct address_space *mapping,
 static int cifs_writepages(struct address_space *mapping,
 			   struct writeback_control *wbc)
 {
-	loff_t start, next;
+	struct cifs_writepages_context ctx = {};
 	int ret;
 
 	/* We have to be careful as we can end up racing with setattr()
@@ -2971,26 +2816,11 @@ static int cifs_writepages(struct address_space *mapping,
 	 * to prevent it.
 	 */
 
-	if (wbc->range_cyclic) {
-		start = mapping->writeback_index * PAGE_SIZE;
-		ret = cifs_writepages_region(mapping, wbc, start, LLONG_MAX, &next);
-		if (ret == 0) {
-			mapping->writeback_index = next / PAGE_SIZE;
-			if (start > 0 && wbc->nr_to_write > 0) {
-				ret = cifs_writepages_region(mapping, wbc, 0,
-							     start, &next);
-				if (ret == 0)
-					mapping->writeback_index =
-						next / PAGE_SIZE;
-			}
-		}
-	} else if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX) {
-		ret = cifs_writepages_region(mapping, wbc, 0, LLONG_MAX, &next);
-		if (wbc->nr_to_write > 0 && ret == 0)
-			mapping->writeback_index = next / PAGE_SIZE;
-	} else {
-		ret = cifs_writepages_region(mapping, wbc,
-					     wbc->range_start, wbc->range_end, &next);
+	ret = write_cache_pages(mapping, wbc, cifs_writepages_add_folio, &ctx);
+	if (ret >= 0 && ctx.begun) {
+		ret = cifs_writepages_submit(mapping, wbc, &ctx);
+		if (ret < 0)
+			return ret;
 	}
 
 	return ret;

cifs test patch to make cifs use its own version of write_cache_pages()

[David Howells]

David Howells <dhowells@redhat.com> wrote:

> And then CIFS. ...
> 
>   Base + Own write_cache_pages():
> 	WRITE: bw=451MiB/s (473MB/s), 113MiB/s-113MiB/s (118MB/s-118MB/s)
> 	WRITE: bw=455MiB/s (478MB/s), 114MiB/s-114MiB/s (119MB/s-120MB/s)
> 	WRITE: bw=453MiB/s (475MB/s), 113MiB/s-113MiB/s (119MB/s-119MB/s)
> 	WRITE: bw=459MiB/s (481MB/s), 115MiB/s-115MiB/s (120MB/s-120MB/s)

Here's my patch to give cifs its own copy of write_cache_pages() so that the
function pointer can be eliminated in case some sort of spectre thing is
causing a slowdown.

This goes on top of "cifs test patch to convert to using write_cache_pages()".

David
---
 fs/cifs/file.c |  137 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 136 insertions(+), 1 deletion(-)

diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 04e2466609d9..c33c7db729c7 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2802,6 +2802,141 @@ static int cifs_writepages_add_folio(struct folio *folio,
 	return 0;
 }
 
+static int cifs_write_cache_pages(struct address_space *mapping,
+				  struct writeback_control *wbc,
+				  struct cifs_writepages_context *ctx)
+{
+	int ret = 0;
+	int done = 0;
+	int error;
+	struct folio_batch fbatch;
+	int nr_folios;
+	pgoff_t index;
+	pgoff_t end;		/* Inclusive */
+	pgoff_t done_index;
+	int range_whole = 0;
+	xa_mark_t tag;
+
+	folio_batch_init(&fbatch);
+	if (wbc->range_cyclic) {
+		index = mapping->writeback_index; /* prev offset */
+		end = -1;
+	} else {
+		index = wbc->range_start >> PAGE_SHIFT;
+		end = wbc->range_end >> PAGE_SHIFT;
+		if (wbc->range_start == 0 && wbc->range_end == LLONG_MAX)
+			range_whole = 1;
+	}
+	if (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages) {
+		tag_pages_for_writeback(mapping, index, end);
+		tag = PAGECACHE_TAG_TOWRITE;
+	} else {
+		tag = PAGECACHE_TAG_DIRTY;
+	}
+	done_index = index;
+	while (!done && (index <= end)) {
+		int i;
+
+		nr_folios = filemap_get_folios_tag(mapping, &index, end,
+				tag, &fbatch);
+
+		if (nr_folios == 0)
+			break;
+
+		for (i = 0; i < nr_folios; i++) {
+			struct folio *folio = fbatch.folios[i];
+
+			done_index = folio->index;
+
+			folio_lock(folio);
+
+			/*
+			 * Page truncated or invalidated. We can freely skip it
+			 * then, even for data integrity operations: the page
+			 * has disappeared concurrently, so there could be no
+			 * real expectation of this data integrity operation
+			 * even if there is now a new, dirty page at the same
+			 * pagecache address.
+			 */
+			if (unlikely(folio->mapping != mapping)) {
+continue_unlock:
+				folio_unlock(folio);
+				continue;
+			}
+
+			if (!folio_test_dirty(folio)) {
+				/* someone wrote it for us */
+				goto continue_unlock;
+			}
+
+			if (folio_test_writeback(folio)) {
+				if (wbc->sync_mode != WB_SYNC_NONE)
+					folio_wait_writeback(folio);
+				else
+					goto continue_unlock;
+			}
+
+			BUG_ON(folio_test_writeback(folio));
+			if (!folio_clear_dirty_for_io(folio))
+				goto continue_unlock;
+
+			error = cifs_writepages_add_folio(folio, wbc, ctx);
+			if (unlikely(error)) {
+				/*
+				 * Handle errors according to the type of
+				 * writeback. There's no need to continue for
+				 * background writeback. Just push done_index
+				 * past this page so media errors won't choke
+				 * writeout for the entire file. For integrity
+				 * writeback, we must process the entire dirty
+				 * set regardless of errors because the fs may
+				 * still have state to clear for each page. In
+				 * that case we continue processing and return
+				 * the first error.
+				 */
+				if (error == AOP_WRITEPAGE_ACTIVATE) {
+					folio_unlock(folio);
+					error = 0;
+				} else if (wbc->sync_mode != WB_SYNC_ALL) {
+					ret = error;
+					done_index = folio->index +
+						folio_nr_pages(folio);
+					done = 1;
+					break;
+				}
+				if (!ret)
+					ret = error;
+			}
+
+			/*
+			 * We stop writing back only if we are not doing
+			 * integrity sync. In case of integrity sync we have to
+			 * keep going until we have written all the pages
+			 * we tagged for writeback prior to entering this loop.
+			 */
+			if (--wbc->nr_to_write <= 0 &&
+			    wbc->sync_mode == WB_SYNC_NONE) {
+				done = 1;
+				break;
+			}
+		}
+		folio_batch_release(&fbatch);
+		cond_resched();
+	}
+
+	/*
+	 * If we hit the last page and there is more work to be done: wrap
+	 * back the index back to the start of the file for the next
+	 * time we are called.
+	 */
+	if (wbc->range_cyclic && !done)
+		done_index = 0;
+	if (wbc->range_cyclic || (range_whole && wbc->nr_to_write > 0))
+		mapping->writeback_index = done_index;
+
+	return ret;
+}
+
 /*
  * Write some of the pending data back to the server
  */
@@ -2816,7 +2951,7 @@ static int cifs_writepages(struct address_space *mapping,
 	 * to prevent it.
 	 */
 
-	ret = write_cache_pages(mapping, wbc, cifs_writepages_add_folio, &ctx);
+	ret = cifs_write_cache_pages(mapping, wbc, &ctx);
 	if (ret >= 0 && ctx.begun) {
 		ret = cifs_writepages_submit(mapping, wbc, &ctx);
 		if (ret < 0)