2022-11-21 17:21:33

by Vlastimil Babka

Subject: [PATCH 05/12] mm, slub: lower the default slub_max_order with CONFIG_SLUB_TINY

With CONFIG_SLUB_TINY we want to minimize memory overhead. By lowering
the default slub_max_order we can make slab allocations use smaller
pages. However depending on object sizes, order-0 might not be the best
due to increased fragmentation. When testing on a 8MB RAM k210 system by
Damien Le Moal [1], slub_max_order=1 had the best results, so use that
as the default for CONFIG_SLUB_TINY.

[1] https://lore.kernel.org/all/[email protected]/

Signed-off-by: Vlastimil Babka <[email protected]>
---
mm/slub.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/mm/slub.c b/mm/slub.c
index 917b79278bad..bf726dd00f7d 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -3888,7 +3888,8 @@ EXPORT_SYMBOL(kmem_cache_alloc_bulk);
* take the list_lock.
*/
static unsigned int slub_min_order;
-static unsigned int slub_max_order = PAGE_ALLOC_COSTLY_ORDER;
+static unsigned int slub_max_order =
+ IS_ENABLED(CONFIG_SLUB_TINY) ? 1 : PAGE_ALLOC_COSTLY_ORDER;
static unsigned int slub_min_objects;

/*
--
2.38.1

2022-11-24 01:31:35

by Roman Gushchin

Subject: Re: [PATCH 05/12] mm, slub: lower the default slub_max_order with CONFIG_SLUB_TINY

On Mon, Nov 21, 2022 at 06:11:55PM +0100, Vlastimil Babka wrote:
> With CONFIG_SLUB_TINY we want to minimize memory overhead. By lowering
> the default slub_max_order we can make slab allocations use smaller
> pages. However depending on object sizes, order-0 might not be the best
> due to increased fragmentation. When testing on a 8MB RAM k210 system by
> Damien Le Moal [1], slub_max_order=1 had the best results, so use that
> as the default for CONFIG_SLUB_TINY.
>
> [1] https://lore.kernel.org/all/[email protected]/
>
> Signed-off-by: Vlastimil Babka <[email protected]>

Acked-by: Roman Gushchin <[email protected]>

Thanks!

2022-11-24 12:06:09

by Hyeonggon Yoo

Subject: Re: [PATCH 05/12] mm, slub: lower the default slub_max_order with CONFIG_SLUB_TINY

On Mon, Nov 21, 2022 at 06:11:55PM +0100, Vlastimil Babka wrote:
> With CONFIG_SLUB_TINY we want to minimize memory overhead. By lowering
> the default slub_max_order we can make slab allocations use smaller
> pages. However depending on object sizes, order-0 might not be the best
> due to increased fragmentation. When testing on a 8MB RAM k210 system by
> Damien Le Moal [1], slub_max_order=1 had the best results, so use that
> as the default for CONFIG_SLUB_TINY.
>
> [1] https://lore.kernel.org/all/[email protected]/
>
> Signed-off-by: Vlastimil Babka <[email protected]>
> ---
> mm/slub.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 917b79278bad..bf726dd00f7d 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -3888,7 +3888,8 @@ EXPORT_SYMBOL(kmem_cache_alloc_bulk);
> * take the list_lock.
> */
> static unsigned int slub_min_order;
> -static unsigned int slub_max_order = PAGE_ALLOC_COSTLY_ORDER;
> +static unsigned int slub_max_order =
> + IS_ENABLED(CONFIG_SLUB_TINY) ? 1 : PAGE_ALLOC_COSTLY_ORDER;
> static unsigned int slub_min_objects;
>
> /*
> --
> 2.38.1
>

Reviewed-by: Hyeonggon Yoo <[email protected]>

--
Thanks,
Hyeonggon