On 22.08.24 00:01, Barry Song wrote:
On Thu, Aug 22, 2024 at 5:39 AM David Hildenbrand <david@xxxxxxxxxx> wrote:
On 12.08.24 00:49, Barry Song wrote:
From: Barry Song <v-songbaohua@xxxxxxxx>
When an mTHP is added to the deferred_list, its partial pages
are unused, leading to wasted memory and potentially increasing
memory reclamation pressure.
Detailing the specifics of how unmapping occurs is quite difficult
and not that useful, so we adopt a simple approach: each time an
mTHP enters the deferred_list, we increment the count by 1; whenever
it leaves for any reason, we decrement the count by 1.
Signed-off-by: Barry Song <v-songbaohua@xxxxxxxx>
---
Documentation/admin-guide/mm/transhuge.rst | 5 +++++
include/linux/huge_mm.h | 1 +
mm/huge_memory.c | 6 ++++++
3 files changed, 12 insertions(+)
diff --git a/Documentation/admin-guide/mm/transhuge.rst b/Documentation/admin-guide/mm/transhuge.rst
index 9fdfb46e4560..7072469de8a8 100644
--- a/Documentation/admin-guide/mm/transhuge.rst
+++ b/Documentation/admin-guide/mm/transhuge.rst
@@ -532,6 +532,11 @@ nr_anon
These huge pages could be entirely mapped or have partially
unmapped/unused subpages.
+nr_split_deferred
+ the number of anon huge pages which have been partially unmapped
+ and put onto split queue. Those unmapped subpages are also unused
+ and temporarily wasting memory.
The name suggests something else ... like a counter of how many have
been deferred split :)
Would "nr_anon_partially_mapped" "nr_anon_split_pending" (or something
less mouthful) be clearer?
(likely "anon" really should be part of the name in any case)
The name we chose (and the implied semantics) will likely have
implications on the handling of Usamas series.
Hi David,
Your point is quite similar to my V1, though not exactly the same. I aimed to
make the name more meaningful for users.
https://lore.kernel.org/all/20240808010457.228753-3-21cnbao@xxxxxxxxx/
Ryan felt that the name should be consistent with the existing split_deferred.
https://lore.kernel.org/all/36e8f1be-868d-4bce-8f32-e2d96b8b7af3@xxxxxxx/#t
Right, it's an increasing counter of how often we added something to the
deferred split queue. It's more like a low-level primitive, although
currently only used for one reason (anon + partial mapping).
It seems that the existing split_deferred may now be less optimal with
Usama's series, as entirely_mapped folios might also be on the list.
Yes.
Ryan is out right now, but I suppose he will be convinced that
"nr_anon_partially_mapped" is probably a better name once
he returns and reviews Usama's series. :-)
Maybe ;) At least it's clear from the name what we are talking about.
--
Cheers,
David / dhildenb
