+ writeback-account-the-number-of-pages-written-back.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

The patch titled
     Subject: writeback: account the number of pages written back
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     writeback-account-the-number-of-pages-written-back.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/writeback-account-the-number-of-pages-written-back.patch

This patch will later appear in the mm-hotfixes-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: account the number of pages written back
Date: Wed, 28 Jun 2023 19:55:48 +0100

nr_to_write is a count of pages, so we need to decrease it by the number
of pages in the folio we just wrote, not by 1.  Most callers specify
either LONG_MAX or 1, so are unaffected, but writeback_sb_inodes() might
end up writing 512x as many pages as it asked for.

Link: https://lkml.kernel.org/r/20230628185548.981888-1-willy@xxxxxxxxxxxxx
Fixes: 793917d997df ("mm/readahead: Add large folio readahead")
Signed-off-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/page-writeback.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

--- a/mm/page-writeback.c~writeback-account-the-number-of-pages-written-back
+++ a/mm/page-writeback.c
@@ -2434,6 +2434,7 @@ int write_cache_pages(struct address_spa
 
 		for (i = 0; i < nr_folios; i++) {
 			struct folio *folio = fbatch.folios[i];
+			unsigned long nr;
 
 			done_index = folio->index;
 
@@ -2471,6 +2472,7 @@ continue_unlock:
 
 			trace_wbc_writepage(wbc, inode_to_bdi(mapping->host));
 			error = writepage(folio, wbc, data);
+			nr = folio_nr_pages(folio);
 			if (unlikely(error)) {
 				/*
 				 * Handle errors according to the type of
@@ -2489,8 +2491,7 @@ continue_unlock:
 					error = 0;
 				} else if (wbc->sync_mode != WB_SYNC_ALL) {
 					ret = error;
-					done_index = folio->index +
-						folio_nr_pages(folio);
+					done_index = folio->index + nr;
 					done = 1;
 					break;
 				}
@@ -2504,7 +2505,8 @@ continue_unlock:
 			 * 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->nr_to_write -= nr;
+			if (wbc->nr_to_write <= 0 &&
 			    wbc->sync_mode == WB_SYNC_NONE) {
 				done = 1;
 				break;
_

Patches currently in -mm which might be from willy@xxxxxxxxxxxxx are

writeback-account-the-number-of-pages-written-back.patch