mm/block/fs: remove laptop_mode

Laptop mode was introduced to save battery, by delaying and consolidating
writes and thereby maximize the time rotating hard drives wouldn't have to
spin.

Luckily, rotating hard drives, with their high spin-up times and power
draw, are a thing of the past for battery-powered devices.  Reclaim has
also since changed to not write single filesystem pages anymore, and
regular filesystem writeback is lumpy by design.

The juice doesn't appear worth the squeeze anymore.  The footprint of the
feature is small, but nevertheless it's a complicating factor in mm,
block, filesystems.  Developers don't think about it, and it likely hasn't
been tested with new reclaim and writeback changes in years.

Let's sunset it.  Keep the sysctl with a deprecation warning around for a
few more cycles, but remove all functionality behind it.

[akpm@linux-foundation.org: fix Documentation/admin-guide/laptops/index.rst]
Link: https://lkml.kernel.org/r/20251216185201.GH905277@cmpxchg.org
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Suggested-by: Christoph Hellwig <hch@infradead.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jens Axboe <axboe@kernel.dk>
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Michal Hocko <mhocko@suse.com>
Cc: Deepanshu Kartikey <kartikey406@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 8 insertions, 22 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 1c87945fa761..fc5691afb998 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -104,13 +104,13 @@ struct scan_control {
 	unsigned int force_deactivate:1;
 	unsigned int skipped_deactivate:1;
 
-	/* Writepage batching in laptop mode; RECLAIM_WRITE */
+	/* zone_reclaim_mode, boost reclaim */
 	unsigned int may_writepage:1;
 
-	/* Can mapped folios be reclaimed? */
+	/* zone_reclaim_mode */
 	unsigned int may_unmap:1;
 
-	/* Can folios be swapped as part of reclaim? */
+	/* zome_reclaim_mode, boost reclaim, cgroup restrictions */
 	unsigned int may_swap:1;
 
 	/* Not allow cache_trim_mode to be turned on as part of reclaim? */
@@ -6365,13 +6365,6 @@ retry:
 
 		if (sc->compaction_ready)
 			break;
-
-		/*
-		 * If we're getting trouble reclaiming, start doing
-		 * writepage even in laptop mode.
-		 */
-		if (sc->priority < DEF_PRIORITY - 2)
-			sc->may_writepage = 1;
 	} while (--sc->priority >= 0);
 
 	last_pgdat = NULL;
@@ -6580,7 +6573,7 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 		.order = order,
 		.nodemask = nodemask,
 		.priority = DEF_PRIORITY,
-		.may_writepage = !laptop_mode,
+		.may_writepage = 1,
 		.may_unmap = 1,
 		.may_swap = 1,
 	};
@@ -6624,7 +6617,7 @@ unsigned long mem_cgroup_shrink_node(struct mem_cgroup *memcg,
 	struct scan_control sc = {
 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
 		.target_mem_cgroup = memcg,
-		.may_writepage = !laptop_mode,
+		.may_writepage = 1,
 		.may_unmap = 1,
 		.reclaim_idx = MAX_NR_ZONES - 1,
 		.may_swap = !noswap,
@@ -6670,7 +6663,7 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 		.reclaim_idx = MAX_NR_ZONES - 1,
 		.target_mem_cgroup = memcg,
 		.priority = DEF_PRIORITY,
-		.may_writepage = !laptop_mode,
+		.may_writepage = 1,
 		.may_unmap = 1,
 		.may_swap = !!(reclaim_options & MEMCG_RECLAIM_MAY_SWAP),
 		.proactive = !!(reclaim_options & MEMCG_RECLAIM_PROACTIVE),
@@ -7051,7 +7044,7 @@ restart:
 		 * from reclaim context. If no pages are reclaimed, the
 		 * reclaim will be aborted.
 		 */
-		sc.may_writepage = !laptop_mode && !nr_boost_reclaim;
+		sc.may_writepage = !nr_boost_reclaim;
 		sc.may_swap = !nr_boost_reclaim;
 
 		/*
@@ -7061,13 +7054,6 @@ restart:
 		 */
 		kswapd_age_node(pgdat, &sc);
 
-		/*
-		 * If we're getting trouble reclaiming, start doing writepage
-		 * even in laptop mode.
-		 */
-		if (sc.priority < DEF_PRIORITY - 2)
-			sc.may_writepage = 1;
-
 		/* Call soft limit reclaim before calling shrink_node. */
 		sc.nr_scanned = 0;
 		nr_soft_scanned = 0;
@@ -7799,7 +7785,7 @@ int user_proactive_reclaim(char *buf,
 				.reclaim_idx = gfp_zone(gfp_mask),
 				.proactive_swappiness = swappiness == -1 ? NULL : &swappiness,
 				.priority = DEF_PRIORITY,
-				.may_writepage = !laptop_mode,
+				.may_writepage = 1,
 				.nr_to_reclaim = max(batch_size, SWAP_CLUSTER_MAX),
 				.may_unmap = 1,
 				.may_swap = 1,