Commit 8356a5a3 authored Jun 25, 2025 by Vlastimil Babka Committed by Andrew Morton Jul 19, 2025

mm, vmstat: remove the NR_WRITEBACK_TEMP node_stat_item counter

The only user of the counter (FUSE) was removed in commit 0c58a97f
("fuse: remove tmp folio for writebacks and internal rb tree") so follow
the established pattern of removing the counter and hardcoding 0 in
meminfo output, as done recently with NR_BOUNCE.  Update documentation for
procfs, including for the value for Bounce that was missed when removing
its counter.

Also remove the mention of NR_WRITEBACK_TEMP implications from a comment
in wb_position_ratio(). The rest of the comment there about fuse setting
bdi->max_ratio to 1% is still correct.

[vbabka@suse.cz: v2]
  Link: https://lkml.kernel.org/r/5a848e15-6a57-4ecb-a015-d4f358b8a5d3@suse.cz
Link: https://lkml.kernel.org/r/20250625-nr_writeback_removal-v1-1-7f2a0df70faa@suse.cz


Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Jeff Layton <jlayton@kernel.org>
Cc: Jeffle Xu <jefflexu@linux.alibaba.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Joanne Koong <joannelkoong@gmail.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Kirill A. Shuemov <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Maxim Patlasov <mpatlasov@parallels.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Miklos Szeredi <mszeredi@redhat.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Zach O'Keefe <zokeefe@google.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

parent ed6a9068

Documentation/filesystems/proc.rst

+5 −3

Original line number	Diff line number	Diff line
		@@ -1196,12 +1196,14 @@ SecPageTables
		Memory consumed by secondary page tables, this currently includes
		KVM mmu and IOMMU allocations on x86 and arm64.
		NFS_Unstable
		Always zero. Previous counted pages which had been written to
		Always zero. Previously counted pages which had been written to
		the server, but has not been committed to stable storage.
		Bounce
		Memory used for block device "bounce buffers"
		Always zero. Previously memory used for block device
		"bounce buffers".
		WritebackTmp
		Memory used by FUSE for temporary writeback buffers
		Always zero. Previously memory used by FUSE for temporary
		writeback buffers.
		CommitLimit
		Based on the overcommit ratio ('vm.overcommit_ratio'),
		this is the total amount of memory currently available to

drivers/base/node.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -500,7 +500,7 @@ static ssize_t node_read_meminfo(struct device *dev,
		nid, K(node_page_state(pgdat, NR_SECONDARY_PAGETABLE)),
		nid, 0UL,
		nid, 0UL,
		nid, K(node_page_state(pgdat, NR_WRITEBACK_TEMP)),
		nid, 0UL,
		nid, K(sreclaimable +
		node_page_state(pgdat, NR_KERNEL_MISC_RECLAIMABLE)),
		nid, K(sreclaimable + sunreclaimable),

fs/proc/meminfo.c

+1 −2

Original line number	Diff line number	Diff line
		@@ -121,8 +121,7 @@ static int meminfo_proc_show(struct seq_file m, void v)

		show_val_kb(m, "NFS_Unstable: ", 0);
		show_val_kb(m, "Bounce: ", 0);
		show_val_kb(m, "WritebackTmp: ",
		global_node_page_state(NR_WRITEBACK_TEMP));
		show_val_kb(m, "WritebackTmp: ", 0);
		show_val_kb(m, "CommitLimit: ", vm_commit_limit());
		show_val_kb(m, "Committed_AS: ", committed);
		seq_printf(m, "VmallocTotal: %8lu kB\n",

include/linux/mmzone.h

+0 −1

Original line number	Diff line number	Diff line
		@@ -206,7 +206,6 @@ enum node_stat_item {
		NR_FILE_PAGES,
		NR_FILE_DIRTY,
		NR_WRITEBACK,
		NR_WRITEBACK_TEMP, /* Writeback using temporary buffers */
		NR_SHMEM, /* shmem pages (included tmpfs/GEM pages) */
		NR_SHMEM_THPS,
		NR_SHMEM_PMDMAPPED,

mm/page-writeback.c

+1 −3

Original line number	Diff line number	Diff line
		@@ -1101,9 +1101,7 @@ static void wb_position_ratio(struct dirty_throttle_control *dtc)
		* such filesystems balance_dirty_pages always checks wb counters
		* against wb limits. Even if global "nr_dirty" is under "freerun".
		* This is especially important for fuse which sets bdi->max_ratio to
		* 1% by default. Without strictlimit feature, fuse writeback may
		* consume arbitrary amount of RAM because it is accounted in
		* NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
		* 1% by default.
		*
		* Here, in wb_position_ratio(), we calculate pos_ratio based on
		* two values: wb_dirty and wb_thresh. Let's consider an example: