[mm-unstable,v1,1/7] mm: multi-gen LRU: section for working set protection

Commit Message

T.J. Alumbaugh Jan. 18, 2023, 12:18 a.m. UTC

Add a section for working set protection in the code and the design
doc. The admin doc already contains its usage.

Signed-off-by: T.J. Alumbaugh <[e-mail]>
---
 Documentation/mm/multigen_lru.rst | 15 +++++++++++++++
 mm/vmscan.c                       |  4 ++++
 2 files changed, 19 insertions(+)

Comments

Matthew Wilcox Jan. 18, 2023, 1 a.m. UTC | #1

On Wed, Jan 18, 2023 at 12:18:21AM +0000, T.J. Alumbaugh wrote:
> +++ b/mm/vmscan.c
> @@ -4475,6 +4475,10 @@ static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long max_seq,
>  	return true;
>  }
>  
> +/******************************************************************************
> + *                          working set protection
> + ******************************************************************************/
> +
>  static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)

We don't usually do this.  Why do you want to?

Patch

diff --git a/Documentation/mm/multigen_lru.rst b/Documentation/mm/multigen_lru.rst
index d8f721f98868..6e1483e70fdc 100644
--- a/Documentation/mm/multigen_lru.rst
+++ b/Documentation/mm/multigen_lru.rst
@@ -141,6 +141,21 @@  loop has detected outlying refaults from the tier this page is in. To
 this end, the feedback loop uses the first tier as the baseline, for
 the reason stated earlier.
 
+Working set protection
+----------------------
+Each generation is timestamped at birth. If ``lru_gen_min_ttl`` is
+set, an ``lruvec`` is protected from the eviction when its oldest
+generation was born within ``lru_gen_min_ttl`` milliseconds. In other
+words, it prevents the working set of ``lru_gen_min_ttl`` milliseconds
+from getting evicted. The OOM killer is triggered if this working set
+cannot be kept in memory.
+
+This time-based approach has the following advantages:
+
+1. It is easier to configure because it is agnostic to applications
+   and memory sizes.
+2. It is more reliable because it is directly wired to the OOM killer.
+
 Summary
 -------
 The multi-gen LRU can be disassembled into the following parts:
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 394ff4962cbc..a741765896b6 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -4475,6 +4475,10 @@  static bool try_to_inc_max_seq(struct lruvec *lruvec, unsigned long max_seq,
 	return true;
 }
 
+/******************************************************************************
+ *                          working set protection
+ ******************************************************************************/
+
 static bool lruvec_is_sizable(struct lruvec *lruvec, struct scan_control *sc)
 {
 	int gen, type, zone;