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authorSergey Senozhatsky <senozhatsky@chromium.org>2023-01-18 03:52:07 +0300
committerAndrew Morton <akpm@linux-foundation.org>2023-02-03 09:33:22 +0300
commit6260ae3583456808dceb4d78077e6388c49ca6d7 (patch)
treefc9d7a6952771eb67bea36e940a43a3f3a3aab9a /mm/zsmalloc.c
parent076cf7ea67010d11a97912423f4cdbeff1bd1f5f (diff)
downloadlinux-6260ae3583456808dceb4d78077e6388c49ca6d7.tar.xz
zsmalloc: rework zspage chain size selection
Patch series "zsmalloc: make zspage chain size configurable". Computers are bad at division. We currently decide the best zspage chain size (max number of physical pages per-zspage) by looking at a `used percentage` value. This is not enough as we lose precision during usage percentage calculations For example, let's look at size class 208: pages per zspage wasted bytes used% 1 144 96 2 80 99 3 16 99 4 160 99 Current algorithm will select 2 page per zspage configuration, as it's the first one to reach 99%. However, 3 pages per zspage waste less memory. Change algorithm and select zspage configuration that has lowest wasted value. Link: https://lkml.kernel.org/r/20230118005210.2814763-1-senozhatsky@chromium.org Link: https://lkml.kernel.org/r/20230118005210.2814763-2-senozhatsky@chromium.org Signed-off-by: Sergey Senozhatsky <senozhatsky@chromium.org> Acked-by: Minchan Kim <minchan@kernel.org> Cc: Mike Kravetz <mike.kravetz@oracle.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/zsmalloc.c')
-rw-r--r--mm/zsmalloc.c56
1 files changed, 19 insertions, 37 deletions
diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
index 9d27d9b00bce..00ab4cca49e4 100644
--- a/mm/zsmalloc.c
+++ b/mm/zsmalloc.c
@@ -822,42 +822,6 @@ out:
return newfg;
}
-/*
- * We have to decide on how many pages to link together
- * to form a zspage for each size class. This is important
- * to reduce wastage due to unusable space left at end of
- * each zspage which is given as:
- * wastage = Zp % class_size
- * usage = Zp - wastage
- * where Zp = zspage size = k * PAGE_SIZE where k = 1, 2, ...
- *
- * For example, for size class of 3/8 * PAGE_SIZE, we should
- * link together 3 PAGE_SIZE sized pages to form a zspage
- * since then we can perfectly fit in 8 such objects.
- */
-static int get_pages_per_zspage(int class_size)
-{
- int i, max_usedpc = 0;
- /* zspage order which gives maximum used size per KB */
- int max_usedpc_order = 1;
-
- for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
- int zspage_size;
- int waste, usedpc;
-
- zspage_size = i * PAGE_SIZE;
- waste = zspage_size % class_size;
- usedpc = (zspage_size - waste) * 100 / zspage_size;
-
- if (usedpc > max_usedpc) {
- max_usedpc = usedpc;
- max_usedpc_order = i;
- }
- }
-
- return max_usedpc_order;
-}
-
static struct zspage *get_zspage(struct page *page)
{
struct zspage *zspage = (struct zspage *)page_private(page);
@@ -2401,6 +2365,24 @@ static int zs_register_shrinker(struct zs_pool *pool)
pool->name);
}
+static int calculate_zspage_chain_size(int class_size)
+{
+ int i, min_waste = INT_MAX;
+ int chain_size = 1;
+
+ for (i = 1; i <= ZS_MAX_PAGES_PER_ZSPAGE; i++) {
+ int waste;
+
+ waste = (i * PAGE_SIZE) % class_size;
+ if (waste < min_waste) {
+ min_waste = waste;
+ chain_size = i;
+ }
+ }
+
+ return chain_size;
+}
+
/**
* zs_create_pool - Creates an allocation pool to work from.
* @name: pool name to be created
@@ -2445,7 +2427,7 @@ struct zs_pool *zs_create_pool(const char *name)
size = ZS_MIN_ALLOC_SIZE + i * ZS_SIZE_CLASS_DELTA;
if (size > ZS_MAX_ALLOC_SIZE)
size = ZS_MAX_ALLOC_SIZE;
- pages_per_zspage = get_pages_per_zspage(size);
+ pages_per_zspage = calculate_zspage_chain_size(size);
objs_per_zspage = pages_per_zspage * PAGE_SIZE / size;
/*