The patch titled
Subject: writeback: rework the loop termination condition in write_cache_pages
has been added to the -mm mm-unstable branch. Its filename is
writeback-rework-the-loop-termination-condition-in-write_cache_pages.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/writeback-rework-the-loop-termination-condition-in-write_cache_pages.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Christoph Hellwig <hch@xxxxxx>
Subject: writeback: rework the loop termination condition in write_cache_pages
Date: Thu, 15 Feb 2024 07:36:41 +0100
Rework the way we deal with the cleanup after the writepage call.
First handle the magic AOP_WRITEPAGE_ACTIVATE separately from real error
returns to get it out of the way of the actual error handling path.
The split the handling on intgrity vs non-integrity branches first, and
return early using a goto for the non-ingegrity early loop condition to
remove the need for the done and done_index local variables, and for
assigning the error to ret when we can just return error directly.
Link: https://lkml.kernel.org/r/20240215063649.2164017-7-hch@xxxxxx
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Dave Chinner <dchinner@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 84 ++++++++++++++++--------------------------
1 file changed, 33 insertions(+), 51 deletions(-)
--- a/mm/page-writeback.c~writeback-rework-the-loop-termination-condition-in-write_cache_pages
+++ a/mm/page-writeback.c
@@ -2396,13 +2396,12 @@ int write_cache_pages(struct address_spa
void *data)
{
int ret = 0;
- int done = 0;
int error;
struct folio_batch fbatch;
+ struct folio *folio;
int nr_folios;
pgoff_t index;
pgoff_t end; /* Inclusive */
- pgoff_t done_index;
xa_mark_t tag;
folio_batch_init(&fbatch);
@@ -2419,8 +2418,7 @@ int write_cache_pages(struct address_spa
} else {
tag = PAGECACHE_TAG_DIRTY;
}
- done_index = index;
- while (!done && (index <= end)) {
+ while (index <= end) {
int i;
nr_folios = filemap_get_folios_tag(mapping, &index, end,
@@ -2430,11 +2428,7 @@ int write_cache_pages(struct address_spa
break;
for (i = 0; i < nr_folios; i++) {
- struct folio *folio = fbatch.folios[i];
- unsigned long nr;
-
- done_index = folio->index;
-
+ folio = fbatch.folios[i];
folio_lock(folio);
/*
@@ -2469,45 +2463,32 @@ continue_unlock:
trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
error = writepage(folio, wbc, data);
- nr = folio_nr_pages(folio);
- wbc->nr_to_write -= nr;
- 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 + nr;
- done = 1;
- break;
- }
- if (!ret)
- ret = error;
+ wbc->nr_to_write -= folio_nr_pages(folio);
+
+ if (error == AOP_WRITEPAGE_ACTIVATE) {
+ folio_unlock(folio);
+ error = 0;
}
/*
- * 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.
+ * For integrity writeback we have to keep going until
+ * we have written all the folios we tagged for
+ * writeback above, even if we run past wbc->nr_to_write
+ * or encounter errors.
+ * We stash away the first error we encounter in
+ * wbc->saved_err so that it can be retrieved when we're
+ * done. This is because the file system may still have
+ * state to clear for each folio.
+ *
+ * For background writeback we exit as soon as we run
+ * past wbc->nr_to_write or encounter the first error.
*/
- done_index = folio->index + nr;
- if (wbc->nr_to_write <= 0 &&
- wbc->sync_mode == WB_SYNC_NONE) {
- done = 1;
- break;
+ if (wbc->sync_mode == WB_SYNC_ALL) {
+ if (error && !ret)
+ ret = error;
+ } else {
+ if (error || wbc->nr_to_write <= 0)
+ goto done;
}
}
folio_batch_release(&fbatch);
@@ -2524,14 +2505,15 @@ continue_unlock:
* of the file if we are called again, which can only happen due to
* -ENOMEM from the file system.
*/
- if (wbc->range_cyclic) {
- if (done)
- mapping->writeback_index = done_index;
- else
- mapping->writeback_index = 0;
- }
-
+ if (wbc->range_cyclic)
+ mapping->writeback_index = 0;
return ret;
+
+done:
+ if (wbc->range_cyclic)
+ mapping->writeback_index = folio->index + folio_nr_pages(folio);
+ folio_batch_release(&fbatch);
+ return error;
}
EXPORT_SYMBOL(write_cache_pages);
_
Patches currently in -mm which might be from hch@xxxxxx are
writeback-dont-call-mapping_set_error-on-aop_writepage_activate.patch
writeback-fix-done_index-when-hitting-the-wbc-nr_to_write.patch
writeback-also-update-wbc-nr_to_write-on-writeback-failure.patch
writeback-only-update-writeback_index-for-range_cyclic-writeback.patch
writeback-rework-the-loop-termination-condition-in-write_cache_pages.patch
writeback-add-a-writeback-iterator.patch
