The patch titled
Subject: writeback: simplify the loops in write_cache_pages()
has been added to the -mm mm-unstable branch. Its filename is
writeback-simplify-the-loops-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-simplify-the-loops-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: "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx>
Subject: writeback: simplify the loops in write_cache_pages()
Date: Thu, 15 Feb 2024 07:36:44 +0100
Collapse the two nested loops into one. This is needed as a step towards
turning this into an iterator.
Note that this drops the "index <= end" check in the previous outer loop
and just relies on filemap_get_folios_tag() to return 0 entries when index
> end. This actually has a subtle implication when end == -1 because then
the returned index will be -1 as well and thus if there is page present on
index -1, we could be looping indefinitely. But as the comment in
filemap_get_folios_tag documents this as already broken anyway we should
not worry about it here either. The fix for that would probably a change
to the filemap_get_folios_tag() calling convention.
[hch@xxxxxx: update the commit log per Jan]
Link: https://lkml.kernel.org/r/20240215063649.2164017-10-hch@xxxxxx
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Acked-by: Dave Chinner <dchinner@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page-writeback.c | 83 ++++++++++++++++++++----------------------
1 file changed, 40 insertions(+), 43 deletions(-)
--- a/mm/page-writeback.c~writeback-simplify-the-loops-in-write_cache_pages
+++ a/mm/page-writeback.c
@@ -2454,6 +2454,7 @@ int write_cache_pages(struct address_spa
int error;
struct folio *folio;
pgoff_t end; /* Inclusive */
+ int i = 0;
if (wbc->range_cyclic) {
wbc->index = mapping->writeback_index; /* prev offset */
@@ -2467,53 +2468,49 @@ int write_cache_pages(struct address_spa
folio_batch_init(&wbc->fbatch);
- while (wbc->index <= end) {
- int i;
-
- writeback_get_batch(mapping, wbc);
-
+ for (;;) {
+ if (i == wbc->fbatch.nr) {
+ writeback_get_batch(mapping, wbc);
+ i = 0;
+ }
if (wbc->fbatch.nr == 0)
break;
- for (i = 0; i < wbc->fbatch.nr; i++) {
- folio = wbc->fbatch.folios[i];
+ folio = wbc->fbatch.folios[i++];
+
+ folio_lock(folio);
+ if (!folio_prepare_writeback(mapping, wbc, folio)) {
+ folio_unlock(folio);
+ continue;
+ }
+
+ trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
+
+ error = writepage(folio, wbc, data);
+ wbc->nr_to_write -= folio_nr_pages(folio);
+
+ if (error == AOP_WRITEPAGE_ACTIVATE) {
+ folio_unlock(folio);
+ error = 0;
+ }
- folio_lock(folio);
- if (!folio_prepare_writeback(mapping, wbc, folio)) {
- folio_unlock(folio);
- continue;
- }
-
- trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
-
- error = writepage(folio, wbc, data);
- wbc->nr_to_write -= folio_nr_pages(folio);
-
- if (error == AOP_WRITEPAGE_ACTIVATE) {
- folio_unlock(folio);
- error = 0;
- }
-
- /*
- * 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.
- */
- if (wbc->sync_mode == WB_SYNC_ALL) {
- if (error && !ret)
- ret = error;
- } else {
- if (error || wbc->nr_to_write <= 0)
- goto done;
- }
+ /*
+ * 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.
+ */
+ if (wbc->sync_mode == WB_SYNC_ALL) {
+ if (error && !ret)
+ ret = error;
+ } else {
+ if (error || wbc->nr_to_write <= 0)
+ goto done;
}
}
_
Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are
memcg-convert-mem_cgroup_move_charge_pte_range-to-use-a-folio.patch
memcg-return-the-folio-in-union-mc_target.patch
memcg-use-a-folio-in-get_mctgt_type.patch
memcg-use-a-folio-in-get_mctgt_type_thp.patch
mm-add-pfn_swap_entry_folio.patch
proc-use-pfn_swap_entry_folio-where-obvious.patch
mprotect-use-pfn_swap_entry_folio.patch
highmem-add-kernel-doc-for-memcpy__folio.patch
rmap-replace-two-calls-to-compound_order-with-folio_order.patch
writeback-remove-a-duplicate-prototype-for-tag_pages_for_writeback.patch
writeback-factor-folio_prepare_writeback-out-of-write_cache_pages.patch
writeback-factor-writeback_get_batch-out-of-write_cache_pages.patch
writeback-simplify-the-loops-in-write_cache_pages.patch
pagevec-add-ability-to-iterate-a-queue.patch
writeback-use-the-folio_batch-queue-iterator.patch
writeback-move-the-folio_prepare_writeback-loop-out-of-write_cache_pages.patch
writeback-remove-a-use-of-write_cache_pages-from-do_writepages.patch
bounds-support-non-power-of-two-config_nr_cpus.patch
