+ mm-fix-ratelimit_pages-update-error-in-dirty_ratio_handler.patch added to mm-hotfixes-unstable branch

+ mm-fix-ratelimit_pages-update-error-in-dirty_ratio_handler.patch added to mm-hotfixes-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm: fix ratelimit_pages update error in dirty_ratio_handler()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-fix-ratelimit_pages-update-error-in-dirty_ratio_handler.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-ratelimit_pages-update-error-in-dirty_ratio_handler.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: Jinliang Zheng <alexjlzheng@tencent.com>
Subject: mm: fix ratelimit_pages update error in dirty_ratio_handler()
Date: Tue, 15 Apr 2025 17:02:32 +0800

In dirty_ratio_handler(), vm_dirty_bytes must be set to zero before
calling writeback_set_ratelimit(), as global_dirty_limits() always
prioritizes the value of vm_dirty_bytes.

That causes ratelimit_pages to still use the value calculated based on
vm_dirty_bytes, which is wrong now.

Link: https://lkml.kernel.org/r/20250415090232.7544-1-alexjlzheng@tencent.com
Fixes: 9d823e8f6b1b ("writeback: per task dirty rate limit")
Signed-off-by: Jinliang Zheng <alexjlzheng@tencent.com>
Reviewed-by: MengEn Sun <mengensun@tencent.com>
Cc: Andrea Righi <andrea@betterlinux.com>
Cc: Fenggaung Wu <fengguang.wu@intel.com>
Cc: Jinliang Zheng <alexjlzheng@tencent.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/page-writeback.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/page-writeback.c~mm-fix-ratelimit_pages-update-error-in-dirty_ratio_handler
+++ a/mm/page-writeback.c
@@ -520,8 +520,8 @@ static int dirty_ratio_handler(const str
 
 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
 	if (ret == 0 && write && vm_dirty_ratio != old_ratio) {
-		writeback_set_ratelimit();
 		vm_dirty_bytes = 0;
+		writeback_set_ratelimit();
 	}
 	return ret;
 }
_

Patches currently in -mm which might be from alexjlzheng@tencent.com are

mm-fix-ratelimit_pages-update-error-in-dirty_ratio_handler.patch