Revert "mm/vmscan: add sysctl knobs for protecting clean cache"

This reverts commit b7017d8.

Documentation/admin-guide/sysctl/vm.rst

@@ -26,8 +26,6 @@ Currently, these files are in /proc/sys/vm:
 
 - admin_reserve_kbytes
 - block_dump
-- clean_low_kbytes
-- clean_min_kbytes
 - compact_memory
 - compaction_proactiveness
 - compact_unevictable_allowed
@@ -115,41 +113,6 @@ block_dump enables block I/O debugging when set to a nonzero value. More
 information on block I/O debugging is in Documentation/admin-guide/laptops/laptop-mode.rst.
 
 
-clean_low_kbytes
-=====================
-
-This knob provides *best-effort* protection of clean file pages. The clean file
-pages on the current node won't be reclaimed under memory pressure when their
-amount is below vm.clean_low_kbytes *unless* we threaten to OOM or have no
-free swap space or vm.swappiness=0.
-
-Protection of clean file pages may be used to prevent thrashing and
-reducing I/O under low-memory conditions.
-
-Setting it to a high value may result in a early eviction of anonymous pages
-into the swap space by attempting to hold the protected amount of clean file
-pages in memory.
-
-The default value is defined by CONFIG_CLEAN_LOW_KBYTES.
-
-
-clean_min_kbytes
-=====================
-
-This knob provides *hard* protection of clean file pages. The clean file pages
-on the current node won't be reclaimed under memory pressure when their amount
-is below vm.clean_min_kbytes.
-
-Hard protection of clean file pages may be used to avoid high latency and
-prevent livelock in near-OOM conditions.
-
-Setting it to a high value may result in a early out-of-memory condition due to
-the inability to reclaim the protected amount of clean file pages when other
-types of pages cannot be reclaimed.
-
-The default value is defined by CONFIG_CLEAN_MIN_KBYTES.
-
-
 compact_memory
 ==============
 

include/linux/mm.h

@@ -202,9 +202,6 @@ static inline void __mm_zero_struct_page(struct page *page)
 
 extern int sysctl_max_map_count;
 
-extern unsigned long sysctl_clean_low_kbytes;
-extern unsigned long sysctl_clean_min_kbytes;
-
 extern unsigned long sysctl_user_reserve_kbytes;
 extern unsigned long sysctl_admin_reserve_kbytes;
 

kernel/sysctl.c

@@ -3113,20 +3113,6 @@ static struct ctl_table vm_table[] = {
 		.extra2		= SYSCTL_ONE,
 	},
 #endif
-	{
-		.procname	= "clean_low_kbytes",
-		.data		= &sysctl_clean_low_kbytes,
-		.maxlen		= sizeof(sysctl_clean_low_kbytes),
-		.mode		= 0644,
-		.proc_handler	= proc_doulongvec_minmax,
-	},
-	{
-		.procname	= "clean_min_kbytes",
-		.data		= &sysctl_clean_min_kbytes,
-		.maxlen		= sizeof(sysctl_clean_min_kbytes),
-		.mode		= 0644,
-		.proc_handler	= proc_doulongvec_minmax,
-	},
 	{
 		.procname	= "user_reserve_kbytes",
 		.data		= &sysctl_user_reserve_kbytes,

mm/Kconfig

@@ -122,41 +122,6 @@ config SPARSEMEM_VMEMMAP
 	  pfn_to_page and page_to_pfn operations.  This is the most
 	  efficient option when sufficient kernel resources are available.
 
-config CLEAN_LOW_KBYTES
-	int "Default value for vm.clean_low_kbytes"
-	depends on SYSCTL
-	default "150000"
-	help
-	  The vm.clean_low_kbytes sysctl knob provides *best-effort*
-	  protection of clean file pages. The clean file pages on the current
-	  node won't be reclaimed under memory pressure when their amount is
-	  below vm.clean_low_kbytes *unless* we threaten to OOM or have
-	  no free swap space or vm.swappiness=0.
-
-	  Protection of clean file pages may be used to prevent thrashing and
-	  reducing I/O under low-memory conditions.
-
-	  Setting it to a high value may result in a early eviction of anonymous
-	  pages into the swap space by attempting to hold the protected amount of
-	  clean file pages in memory.
-
-config CLEAN_MIN_KBYTES
-	int "Default value for vm.clean_min_kbytes"
-	depends on SYSCTL
-	default "0"
-	help
-	  The vm.clean_min_kbytes sysctl knob provides *hard* protection
-	  of clean file pages. The clean file pages on the current node won't be
-	  reclaimed under memory pressure when their amount is below
-	  vm.clean_min_kbytes.
-
-	  Hard protection of clean file pages may be used to avoid high latency and
-	  prevent livelock in near-OOM conditions.
-
-	  Setting it to a high value may result in a early out-of-memory condition
-	  due to the inability to reclaim the protected amount of clean file pages
-	  when other types of pages cannot be reclaimed.
-
 config HAVE_MEMBLOCK_PHYS_MAP
 	bool
 

mm/vmscan.c

@@ -120,19 +120,6 @@ struct scan_control {
 	/* The file pages on the current node are dangerously low */
 	unsigned int file_is_tiny:1;
 
-	/*
-	 * The clean file pages on the current node won't be reclaimed when
-	 * their amount is below vm.clean_low_kbytes *unless* we threaten
-	 * to OOM or have no free swap space or vm.swappiness=0.
-	 */
-	unsigned int clean_below_low:1;
-
-	/*
-	 * The clean file pages on the current node won't be reclaimed when
-	 * their amount is below vm.clean_min_kbytes.
-	 */
-	unsigned int clean_below_min:1;
-
 	/* Allocation order */
 	s8 order;
 
@@ -179,17 +166,6 @@ struct scan_control {
 #define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
 #endif
 
-#if CONFIG_CLEAN_LOW_KBYTES < 0
-#error "CONFIG_CLEAN_LOW_KBYTES must be >= 0"
-#endif
-
-#if CONFIG_CLEAN_MIN_KBYTES < 0
-#error "CONFIG_CLEAN_MIN_KBYTES must be >= 0"
-#endif
-
-unsigned long sysctl_clean_low_kbytes __read_mostly = CONFIG_CLEAN_LOW_KBYTES;
-unsigned long sysctl_clean_min_kbytes __read_mostly = CONFIG_CLEAN_MIN_KBYTES;
-
 /*
  * From 0 .. 200.  Higher means more swappy.
  */
@@ -2304,16 +2280,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
 		goto out;
 	}
 
-	/*
-	 * Force-scan anon if clean file pages is under vm.clean_min_kbytes
-	 * or vm.clean_low_kbytes (unless the swappiness setting
-	 * disagrees with swapping).
-	 */
-	if ((sc->clean_below_low || sc->clean_below_min) && swappiness) {
-		scan_balance = SCAN_ANON;
-		goto out;
-	}
-
 	/*
 	 * If there is enough inactive page cache, we do not reclaim
 	 * anything from the anonymous working right now.
@@ -2450,13 +2416,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
 			BUG();
 		}
 
-		/*
-		 * Don't reclaim clean file pages when their amount is below
-		 * vm.clean_min_kbytes.
-		 */
-		if (file && sc->clean_below_min)
-			scan = 0;
-
 		nr[lru] = scan;
 	}
 }
@@ -2807,34 +2766,6 @@ static void shrink_node(pg_data_t *pgdat, struct scan_control *sc)
 			anon >> sc->priority;
 	}
 
-	/*
-	 * Check the number of clean file pages to protect them from
-	 * reclaiming if their amount is below the specified.
-	 */
-	if (sysctl_clean_low_kbytes || sysctl_clean_min_kbytes) {
-		unsigned long reclaimable_file, dirty, clean;
-
-		reclaimable_file =
-			node_page_state(pgdat, NR_ACTIVE_FILE) +
-			node_page_state(pgdat, NR_INACTIVE_FILE) +
-			node_page_state(pgdat, NR_ISOLATED_FILE);
-		dirty = node_page_state(pgdat, NR_FILE_DIRTY);
-		/*
-		 * node_page_state() sum can go out of sync since
-		 * all the values are not read at once.
-		 */
-		if (likely(reclaimable_file > dirty))
-			clean = (reclaimable_file - dirty) << (PAGE_SHIFT - 10);
-		else
-			clean = 0;
-
-		sc->clean_below_low = clean < sysctl_clean_low_kbytes;
-		sc->clean_below_min = clean < sysctl_clean_min_kbytes;
-	} else {
-		sc->clean_below_low = false;
-		sc->clean_below_min = false;
-	}
-
 	shrink_node_memcgs(pgdat, sc);
 
 	if (reclaim_state) {