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Revert "mm/vmscan: add sysctl knobs for protecting the working set"
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This reverts commit 69231fa.
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@xanmod
xanmod committed Aug 6, 2022
1 parent f299573 commit ab65c0b
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66 changes: 0 additions & 66 deletions Documentation/admin-guide/sysctl/vm.rst
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Original file line number Diff line number Diff line change
Expand Up @@ -25,9 +25,6 @@ files can be found in mm/swap.c.
Currently, these files are in /proc/sys/vm:

- admin_reserve_kbytes
- anon_min_kbytes
- clean_low_kbytes
- clean_min_kbytes
- compact_memory
- compaction_proactiveness
- compact_unevictable_allowed
Expand Down Expand Up @@ -109,61 +106,6 @@ On x86_64 this is about 128MB.
Changing this takes effect whenever an application requests memory.


anon_min_kbytes
===============

This knob provides *hard* protection of anonymous pages. The anonymous pages
on the current node won't be reclaimed under any conditions when their amount
is below vm.anon_min_kbytes.

This knob may be used to prevent excessive swap thrashing when anonymous
memory is low (for example, when memory is going to be overfilled by
compressed data of zram module).

Setting this value too high (close to MemTotal) can result in inability to
swap and can lead to early OOM under memory pressure.

The default value is defined by CONFIG_ANON_MIN_KBYTES.


clean_low_kbytes
================

This knob provides *best-effort* protection of clean file pages. The file pages
on the current node won't be reclaimed under memory pressure when the amount of
clean file pages is below vm.clean_low_kbytes *unless* we threaten to OOM.

Protection of clean file pages using this knob may be used when swapping is
still possible to
- prevent disk I/O thrashing under memory pressure;
- improve performance in disk cache-bound tasks under memory pressure.

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 file pages on the
current node won't be reclaimed under memory pressure when the amount of clean
file pages is below vm.clean_min_kbytes.

Hard protection of clean file pages using this knob may be used to
- prevent disk I/O thrashing under memory pressure even with no free swap space;
- improve performance in disk cache-bound tasks under memory pressure;
- 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
==============

Expand Down Expand Up @@ -970,14 +912,6 @@ be 133 (x + 2x = 200, 2x = 133.33).
At 0, the kernel will not initiate swap until the amount of free and
file-backed pages is less than the high watermark in a zone.

This knob has no effect if the amount of clean file pages on the current
node is below vm.clean_low_kbytes or vm.clean_min_kbytes. In this case,
only anonymous pages can be reclaimed.

If the number of anonymous pages on the current node is below
vm.anon_min_kbytes, then only file pages can be reclaimed with
any vm.swappiness value.


unprivileged_userfaultfd
========================
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4 changes: 0 additions & 4 deletions include/linux/mm.h
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Expand Up @@ -196,10 +196,6 @@ static inline void __mm_zero_struct_page(struct page *page)

extern int sysctl_max_map_count;

extern unsigned long sysctl_anon_min_kbytes;
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;

Expand Down
21 changes: 0 additions & 21 deletions kernel/sysctl.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2380,27 +2380,6 @@ static struct ctl_table vm_table[] = {
.extra2 = SYSCTL_ONE,
},
#endif
{
.procname = "anon_min_kbytes",
.data = &sysctl_anon_min_kbytes,
.maxlen = sizeof(unsigned long),
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
},
{
.procname = "clean_low_kbytes",
.data = &sysctl_clean_low_kbytes,
.maxlen = sizeof(unsigned long),
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
},
{
.procname = "clean_min_kbytes",
.data = &sysctl_clean_min_kbytes,
.maxlen = sizeof(unsigned long),
.mode = 0644,
.proc_handler = proc_doulongvec_minmax,
},
{
.procname = "user_reserve_kbytes",
.data = &sysctl_user_reserve_kbytes,
Expand Down
63 changes: 0 additions & 63 deletions mm/Kconfig
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Original file line number Diff line number Diff line change
Expand Up @@ -441,69 +441,6 @@ config SPARSEMEM_VMEMMAP
pfn_to_page and page_to_pfn operations. This is the most
efficient option when sufficient kernel resources are available.

config ANON_MIN_KBYTES
int "Default value for vm.anon_min_kbytes"
depends on SYSCTL
range 0 4294967295
default 0
help
This option sets the default value for vm.anon_min_kbytes sysctl knob.

The vm.anon_min_kbytes sysctl knob provides *hard* protection of
anonymous pages. The anonymous pages on the current node won't be
reclaimed under any conditions when their amount is below
vm.anon_min_kbytes. This knob may be used to prevent excessive swap
thrashing when anonymous memory is low (for example, when memory is
going to be overfilled by compressed data of zram module).

Setting this value too high (close to MemTotal) can result in
inability to swap and can lead to early OOM under memory pressure.

config CLEAN_LOW_KBYTES
int "Default value for vm.clean_low_kbytes"
depends on SYSCTL
range 0 4294967295
default 0
help
This option sets the default value for vm.clean_low_kbytes sysctl knob.

The vm.clean_low_kbytes sysctl knob provides *best-effort*
protection of clean file pages. The file pages on the current node
won't be reclaimed under memory pressure when the amount of clean file
pages is below vm.clean_low_kbytes *unless* we threaten to OOM.
Protection of clean file pages using this knob may be used when
swapping is still possible to
- prevent disk I/O thrashing under memory pressure;
- improve performance in disk cache-bound tasks under memory
pressure.

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
range 0 4294967295
default 0
help
This option sets the default value for vm.clean_min_kbytes sysctl knob.

The vm.clean_min_kbytes sysctl knob provides *hard* protection of
clean file pages. The file pages on the current node won't be
reclaimed under memory pressure when the amount of clean file pages is
below vm.clean_min_kbytes. Hard protection of clean file pages using
this knob may be used to
- prevent disk I/O thrashing under memory pressure even with no free
swap space;
- improve performance in disk cache-bound tasks under memory
pressure;
- 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

Expand Down
91 changes: 0 additions & 91 deletions mm/vmscan.c
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Original file line number Diff line number Diff line change
Expand Up @@ -128,15 +128,6 @@ struct scan_control {
/* The file pages on the current node are dangerously low */
unsigned int file_is_tiny:1;

/* The anonymous pages on the current node are below vm.anon_min_kbytes */
unsigned int anon_below_min:1;

/* The clean file pages on the current node are below vm.clean_low_kbytes */
unsigned int clean_below_low:1;

/* The clean file pages on the current node are below vm.clean_min_kbytes */
unsigned int clean_below_min:1;

/* Always discard instead of demoting to lower tier memory */
unsigned int no_demotion:1;

Expand Down Expand Up @@ -193,10 +184,6 @@ struct scan_control {
#define prefetchw_prev_lru_page(_page, _base, _field) do { } while (0)
#endif

unsigned long sysctl_anon_min_kbytes __read_mostly = CONFIG_ANON_MIN_KBYTES;
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.
*/
Expand Down Expand Up @@ -2701,54 +2688,6 @@ enum scan_balance {
SCAN_FILE,
};

static void prepare_workingset_protection(pg_data_t *pgdat, struct scan_control *sc)
{
/*
* Check the number of anonymous pages to protect them from
* reclaiming if their amount is below the specified.
*/
if (sysctl_anon_min_kbytes) {
unsigned long reclaimable_anon;

reclaimable_anon =
node_page_state(pgdat, NR_ACTIVE_ANON) +
node_page_state(pgdat, NR_INACTIVE_ANON) +
node_page_state(pgdat, NR_ISOLATED_ANON);
reclaimable_anon <<= (PAGE_SHIFT - 10);

sc->anon_below_min = reclaimable_anon < sysctl_anon_min_kbytes;
} else
sc->anon_below_min = 0;

/*
* 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 = 0;
sc->clean_below_min = 0;
}
}

static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc)
{
unsigned long file;
Expand Down Expand Up @@ -2853,8 +2792,6 @@ static void prepare_scan_count(pg_data_t *pgdat, struct scan_control *sc)
!(sc->may_deactivate & DEACTIVATE_ANON) &&
anon >> sc->priority;
}

prepare_workingset_protection(pgdat, sc);
}

/*
Expand Down Expand Up @@ -2913,15 +2850,6 @@ 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_low_kbytes
* or vm.clean_min_kbytes.
*/
if (sc->clean_below_low || sc->clean_below_min) {
scan_balance = SCAN_ANON;
goto out;
}

/*
* If there is enough inactive page cache, we do not reclaim
* anything from the anonymous working right now.
Expand Down Expand Up @@ -3066,25 +2994,6 @@ static void get_scan_count(struct lruvec *lruvec, struct scan_control *sc,
BUG();
}

/*
* Hard protection of the working set.
*/
if (file) {
/*
* Don't reclaim file pages when the amount of
* clean file pages is below vm.clean_min_kbytes.
*/
if (sc->clean_below_min)
scan = 0;
} else {
/*
* Don't reclaim anonymous pages when their
* amount is below vm.anon_min_kbytes.
*/
if (sc->anon_below_min)
scan = 0;
}

nr[lru] = scan;
}
}
Expand Down

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