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Message-ID: <2214157.1677250083@warthog.procyon.org.uk>
Date: Fri, 24 Feb 2023 14:48:03 +0000
From: David Howells <dhowells@...hat.com>
To: Linus Torvalds <torvalds@...ux-foundation.org>,
Steve French <stfrench@...rosoft.com>
Cc: dhowells@...hat.com, Vishal Moola <vishal.moola@...il.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Jan Kara <jack@...e.cz>, Paulo Alcantara <pc@....nz>,
Matthew Wilcox <willy@...radead.org>,
Huang Ying <ying.huang@...el.com>,
Baolin Wang <baolin.wang@...ux.alibaba.com>,
Xin Hao <xhao@...ux.alibaba.com>, linux-mm@...ck.org,
mm-commits@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [RFC][PATCH] cifs, afs: Revert changes to {cifs,afs}_writepages_region()
Here's a more complex patch that reverts Vishal's patch to afs and your
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. An alternative way
of doing this would be to make filemap_get_folios_tag() take a limit count.
This is likely to be more efficient for the common case as
*_extend_writeback() will deal with pages that are contiguous to the
starting page before we get on to continuing to process the batch.
For filemap_get_folios_tag() to be of use, the batch has to be passed down,
and if it contains scattered, non-contiguous pages, these are likely to end
up being pinned by the batch for significant periods of time whilst I/O is
undertaken on earlier pages.
Fix: 3822a7c40997 ("Merge tag 'mm-stable-2023-02-20-13-37' of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm")
Fix: acc8d8588cb7 ("afs: convert afs_writepages_region() to use filemap_get_folios_tag()")
Signed-off-by: David Howells <dhowells@...hat.com>
---
fs/afs/write.c | 116 +++++++++++++++++++++++-------------------------
fs/cifs/file.c | 114 ++++++++++++++++++++---------------------------
include/linux/pagemap.h | 2
mm/filemap.c | 58 ++++++++++++++++++++++++
4 files changed, 165 insertions(+), 125 deletions(-)
diff --git a/fs/afs/write.c b/fs/afs/write.c
index 571f3b9a417e..b04a95262c4f 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;
_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);
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 5365a3299088..121254086e30 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -2857,92 +2857,76 @@ 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)) {
- folio_unlock(folio);
- goto skip_write;
+ } 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);
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:
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