2022-02-21 18:51:47

by Hyeonggon Yoo

Subject: [PATCH 4/5] mm/slub: Limit min_partial only in cache creation

SLUB sets number of minimum partial slabs for node (min_partial) using
set_min_partial(). SLUB holds at least min_partial slabs even if they're empty
to avoid excessive use of page allocator.

set_min_partial() limits value of min_partial between MIN_PARTIAL and
MAX_PARTIAL. As set_min_partial() can be called by min_partial_store()
too, Only limit value of min_partial in kmem_cache_open() so that it
can be changed to value that a user wants.

Signed-off-by: Hyeonggon Yoo <[email protected]>
---
mm/slub.c | 11 ++++++-----
1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index 3a4458976ab7..a4964deccb61 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -4002,10 +4002,6 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)

static void set_min_partial(struct kmem_cache *s, unsigned long min)
{
- if (min < MIN_PARTIAL)
- min = MIN_PARTIAL;
- else if (min > MAX_PARTIAL)
- min = MAX_PARTIAL;
s->min_partial = min;
}

@@ -4184,6 +4180,8 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)

static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
{
+ int min_partial;
+
s->flags = kmem_cache_flags(s->size, flags, s->name);
#ifdef CONFIG_SLAB_FREELIST_HARDENED
s->random = get_random_long();
@@ -4215,7 +4213,10 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
* The larger the object size is, the more slabs we want on the partial
* list to avoid pounding the page allocator excessively.
*/
- set_min_partial(s, ilog2(s->size) / 2);
+ min_partial = min(MAX_PARTIAL, ilog2(s->size) / 2);
+ min_partial = max(MIN_PARTIAL, min_partial);
+
+ set_min_partial(s, min_partial);

set_cpu_partial(s);

--
2.33.1

2022-02-23 02:32:17

by David Rientjes

Subject: Re: [PATCH 4/5] mm/slub: Limit min_partial only in cache creation

On Mon, 21 Feb 2022, Hyeonggon Yoo wrote:

> SLUB sets number of minimum partial slabs for node (min_partial) using
> set_min_partial(). SLUB holds at least min_partial slabs even if they're empty
> to avoid excessive use of page allocator.
>
> set_min_partial() limits value of min_partial between MIN_PARTIAL and
> MAX_PARTIAL. As set_min_partial() can be called by min_partial_store()
> too, Only limit value of min_partial in kmem_cache_open() so that it
> can be changed to value that a user wants.
>
> Signed-off-by: Hyeonggon Yoo <[email protected]>

I think this makes sense and there is no reason to limit the bounds that
may be set at runtime with undocumented behavior.

However, since set_min_partial() is only setting the value in the
kmem_cache, could we remove the helper function entirely and fold it into
its two callers?

> ---
> mm/slub.c | 11 ++++++-----
> 1 file changed, 6 insertions(+), 5 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 3a4458976ab7..a4964deccb61 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -4002,10 +4002,6 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
>
> static void set_min_partial(struct kmem_cache *s, unsigned long min)
> {
> - if (min < MIN_PARTIAL)
> - min = MIN_PARTIAL;
> - else if (min > MAX_PARTIAL)
> - min = MAX_PARTIAL;
> s->min_partial = min;
> }
>
> @@ -4184,6 +4180,8 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
>
> static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
> {
> + int min_partial;
> +
> s->flags = kmem_cache_flags(s->size, flags, s->name);
> #ifdef CONFIG_SLAB_FREELIST_HARDENED
> s->random = get_random_long();
> @@ -4215,7 +4213,10 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
> * The larger the object size is, the more slabs we want on the partial
> * list to avoid pounding the page allocator excessively.
> */
> - set_min_partial(s, ilog2(s->size) / 2);
> + min_partial = min(MAX_PARTIAL, ilog2(s->size) / 2);
> + min_partial = max(MIN_PARTIAL, min_partial);
> +
> + set_min_partial(s, min_partial);
>
> set_cpu_partial(s);
>
> --
> 2.33.1
>
>

2022-02-23 11:49:05

by Hyeonggon Yoo

Subject: Re: [PATCH 4/5] mm/slub: Limit min_partial only in cache creation

On Tue, Feb 22, 2022 at 03:48:16PM -0800, David Rientjes wrote:
> On Mon, 21 Feb 2022, Hyeonggon Yoo wrote:
>
> > SLUB sets number of minimum partial slabs for node (min_partial) using
> > set_min_partial(). SLUB holds at least min_partial slabs even if they're empty
> > to avoid excessive use of page allocator.
> >
> > set_min_partial() limits value of min_partial between MIN_PARTIAL and
> > MAX_PARTIAL. As set_min_partial() can be called by min_partial_store()
> > too, Only limit value of min_partial in kmem_cache_open() so that it
> > can be changed to value that a user wants.
> >
> > Signed-off-by: Hyeonggon Yoo <[email protected]>
>
> I think this makes sense and there is no reason to limit the bounds that
> may be set at runtime with undocumented behavior.

Thank you for comment.

>
> However, since set_min_partial() is only setting the value in the
> kmem_cache, could we remove the helper function entirely and fold it into
> its two callers?

Right. We don't need to separate this as function. I'll update this
in next version. Thanks!

>
> > ---
> > mm/slub.c | 11 ++++++-----
> > 1 file changed, 6 insertions(+), 5 deletions(-)
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 3a4458976ab7..a4964deccb61 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -4002,10 +4002,6 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
> >
> > static void set_min_partial(struct kmem_cache *s, unsigned long min)
> > {
> > - if (min < MIN_PARTIAL)
> > - min = MIN_PARTIAL;
> > - else if (min > MAX_PARTIAL)
> > - min = MAX_PARTIAL;
> > s->min_partial = min;
> > }
> >
> > @@ -4184,6 +4180,8 @@ static int calculate_sizes(struct kmem_cache *s, int forced_order)
> >
> > static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
> > {
> > + int min_partial;
> > +
> > s->flags = kmem_cache_flags(s->size, flags, s->name);
> > #ifdef CONFIG_SLAB_FREELIST_HARDENED
> > s->random = get_random_long();
> > @@ -4215,7 +4213,10 @@ static int kmem_cache_open(struct kmem_cache *s, slab_flags_t flags)
> > * The larger the object size is, the more slabs we want on the partial
> > * list to avoid pounding the page allocator excessively.
> > */
> > - set_min_partial(s, ilog2(s->size) / 2);
> > + min_partial = min(MAX_PARTIAL, ilog2(s->size) / 2);
> > + min_partial = max(MIN_PARTIAL, min_partial);
> > +
> > + set_min_partial(s, min_partial);
> >
> > set_cpu_partial(s);
> >
> > --
> > 2.33.1
> >
> >

--
Hyeonggon

2022-02-24 15:24:15

by Vlastimil Babka

Subject: Re: [PATCH 4/5] mm/slub: Limit min_partial only in cache creation

On 2/23/22 04:37, Hyeonggon Yoo wrote:
> On Tue, Feb 22, 2022 at 03:48:16PM -0800, David Rientjes wrote:
>> On Mon, 21 Feb 2022, Hyeonggon Yoo wrote:
>>
>> > SLUB sets number of minimum partial slabs for node (min_partial) using
>> > set_min_partial(). SLUB holds at least min_partial slabs even if they're empty
>> > to avoid excessive use of page allocator.
>> >
>> > set_min_partial() limits value of min_partial between MIN_PARTIAL and
>> > MAX_PARTIAL. As set_min_partial() can be called by min_partial_store()
>> > too, Only limit value of min_partial in kmem_cache_open() so that it
>> > can be changed to value that a user wants.
>> >
>> > Signed-off-by: Hyeonggon Yoo <[email protected]>
>>
>> I think this makes sense and there is no reason to limit the bounds that
>> may be set at runtime with undocumented behavior.

Right.

> Thank you for comment.
>
>>
>> However, since set_min_partial() is only setting the value in the
>> kmem_cache, could we remove the helper function entirely and fold it into
>> its two callers?
>
> Right. We don't need to separate this as function. I'll update this
> in next version. Thanks!

Agreed, thanks!