2024-03-12 14:05:58

by Xiongwei Song

Subject: [PATCH v2] mm/slub: Simplify get_partial_node()

From: Xiongwei Song <[email protected]>

Remove the check of !kmem_cache_has_cpu_partial() because it is always
false, we've known this by calling kmem_cache_debug() before calling
remove_partial(), so we can remove the check.

Meanwhile, redo filling cpu partial and add comment to improve the
readability.

Signed-off-by: Xiongwei Song <[email protected]>
---
Changes in v2:
- Use "#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)" to instead
"if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))" to fix build error.
(Thanks Chengming Zhou)
- Add __maybe_unused for partial_slabs to prevent compiler warning.

v1:
https://lore.kernel.org/linux-kernel/[email protected]/T/
---
mm/slub.c | 24 +++++++++++++-----------
1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/mm/slub.c b/mm/slub.c
index a3ab096c38c0..ab526960ee5b 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2588,7 +2588,7 @@ static struct slab *get_partial_node(struct kmem_cache *s,
{
struct slab *slab, *slab2, *partial = NULL;
unsigned long flags;
- unsigned int partial_slabs = 0;
+ unsigned int __maybe_unused partial_slabs = 0;

/*
* Racy check. If we mistakenly see no partial slabs then we
@@ -2620,19 +2620,21 @@ static struct slab *get_partial_node(struct kmem_cache *s,
if (!partial) {
partial = slab;
stat(s, ALLOC_FROM_PARTIAL);
- } else {
- put_cpu_partial(s, slab, 0);
- stat(s, CPU_PARTIAL_NODE);
- partial_slabs++;
+
+ /* Fill cpu partial if needed from next iteration, or break */
+ if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))
+ continue;
+ else
+ break;
}
-#ifdef CONFIG_SLUB_CPU_PARTIAL
- if (!kmem_cache_has_cpu_partial(s)
- || partial_slabs > s->cpu_partial_slabs / 2)
+
+#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)
+ put_cpu_partial(s, slab, 0);
+ stat(s, CPU_PARTIAL_NODE);
+
+ if (++partial_slabs > s->cpu_partial_slabs/2)
break;
-#else
- break;
#endif
-
}
spin_unlock_irqrestore(&n->list_lock, flags);
return partial;
--
2.34.1

2024-03-12 15:23:37

by Chengming Zhou

Subject: Re: [PATCH v2] mm/slub: Simplify get_partial_node()

On 2024/3/12 22:05, [email protected] wrote:
> From: Xiongwei Song <[email protected]>
>
> Remove the check of !kmem_cache_has_cpu_partial() because it is always
> false, we've known this by calling kmem_cache_debug() before calling
> remove_partial(), so we can remove the check.
>
> Meanwhile, redo filling cpu partial and add comment to improve the
> readability.
>
> Signed-off-by: Xiongwei Song <[email protected]>
> ---
> Changes in v2:
> - Use "#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)" to instead
> "if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))" to fix build error.
> (Thanks Chengming Zhou)
> - Add __maybe_unused for partial_slabs to prevent compiler warning.
>
> v1:
> https://lore.kernel.org/linux-kernel/[email protected]/T/
> ---
> mm/slub.c | 24 +++++++++++++-----------
> 1 file changed, 13 insertions(+), 11 deletions(-)
>
> diff --git a/mm/slub.c b/mm/slub.c
> index a3ab096c38c0..ab526960ee5b 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2588,7 +2588,7 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> {
> struct slab *slab, *slab2, *partial = NULL;
> unsigned long flags;
> - unsigned int partial_slabs = 0;
> + unsigned int __maybe_unused partial_slabs = 0;
>
> /*
> * Racy check. If we mistakenly see no partial slabs then we
> @@ -2620,19 +2620,21 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> if (!partial) {
> partial = slab;
> stat(s, ALLOC_FROM_PARTIAL);
> - } else {
> - put_cpu_partial(s, slab, 0);
> - stat(s, CPU_PARTIAL_NODE);
> - partial_slabs++;
> +
> + /* Fill cpu partial if needed from next iteration, or break */
> + if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))
> + continue;
> + else
> + break;
> }
> -#ifdef CONFIG_SLUB_CPU_PARTIAL
> - if (!kmem_cache_has_cpu_partial(s)
> - || partial_slabs > s->cpu_partial_slabs / 2)
> +
> +#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)

Hmm, these two CONFIG_SLUB_CPU_PARTIAL look verbose to me :(

How about using just one, maybe like this?

diff --git a/mm/slub.c b/mm/slub.c
index 2ef88bbf56a3..a018c715b648 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2620,19 +2620,16 @@ static struct slab *get_partial_node(struct kmem_cache *s,
if (!partial) {
partial = slab;
stat(s, ALLOC_FROM_PARTIAL);
+#ifdef CONFIG_SLUB_CPU_PARTIAL
} else {
put_cpu_partial(s, slab, 0);
stat(s, CPU_PARTIAL_NODE);
- partial_slabs++;
- }
-#ifdef CONFIG_SLUB_CPU_PARTIAL
- if (!kmem_cache_has_cpu_partial(s)
- || partial_slabs > s->cpu_partial_slabs / 2)
- break;
+ if (++partial_slabs > s->cpu_partial_slabs / 2)
+ break;
#else
- break;
+ break;
#endif
-
+ }
}
spin_unlock_irqrestore(&n->list_lock, flags);
return partial;


> + put_cpu_partial(s, slab, 0);
> + stat(s, CPU_PARTIAL_NODE);
> +
> + if (++partial_slabs > s->cpu_partial_slabs/2)
> break;
> -#else
> - break;
> #endif
> -
> }
> spin_unlock_irqrestore(&n->list_lock, flags);
> return partial;

2024-03-13 06:16:34

by Song, Xiongwei

Subject: RE: [PATCH v2] mm/slub: Simplify get_partial_node()

> On 2024/3/12 22:05, [email protected] wrote:
> > From: Xiongwei Song <[email protected]>
> >
> > Remove the check of !kmem_cache_has_cpu_partial() because it is always
> > false, we've known this by calling kmem_cache_debug() before calling
> > remove_partial(), so we can remove the check.
> >
> > Meanwhile, redo filling cpu partial and add comment to improve the
> > readability.
> >
> > Signed-off-by: Xiongwei Song <[email protected]>
> > ---
> > Changes in v2:
> > - Use "#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)" to instead
> > "if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))" to fix build error.
> > (Thanks Chengming Zhou)
> > - Add __maybe_unused for partial_slabs to prevent compiler warning.
> >
> > v1:
> > https://lore.kernel.org/linux-kernel/[email protected]/T/
> > ---
> > mm/slub.c | 24 +++++++++++++-----------
> > 1 file changed, 13 insertions(+), 11 deletions(-)
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index a3ab096c38c0..ab526960ee5b 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -2588,7 +2588,7 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> > {
> > struct slab *slab, *slab2, *partial = NULL;
> > unsigned long flags;
> > - unsigned int partial_slabs = 0;
> > + unsigned int __maybe_unused partial_slabs = 0;
> >
> > /*
> > * Racy check. If we mistakenly see no partial slabs then we
> > @@ -2620,19 +2620,21 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> > if (!partial) {
> > partial = slab;
> > stat(s, ALLOC_FROM_PARTIAL);
> > - } else {
> > - put_cpu_partial(s, slab, 0);
> > - stat(s, CPU_PARTIAL_NODE);
> > - partial_slabs++;
> > +
> > + /* Fill cpu partial if needed from next iteration, or break */
> > + if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))
> > + continue;
> > + else
> > + break;
> > }
> > -#ifdef CONFIG_SLUB_CPU_PARTIAL
> > - if (!kmem_cache_has_cpu_partial(s)
> > - || partial_slabs > s->cpu_partial_slabs / 2)
> > +
> > +#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)
>
> Hmm, these two CONFIG_SLUB_CPU_PARTIAL look verbose to me :(
>
> How about using just one, maybe like this?
>
> diff --git a/mm/slub.c b/mm/slub.c
> index 2ef88bbf56a3..a018c715b648 100644
> --- a/mm/slub.c
> +++ b/mm/slub.c
> @@ -2620,19 +2620,16 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> if (!partial) {
> partial = slab;
> stat(s, ALLOC_FROM_PARTIAL);
> +#ifdef CONFIG_SLUB_CPU_PARTIAL
> } else {

I don't like splitting "if...else..." up with preprocessor directives personally. It's messy for me.

2024-03-13 23:36:35

by David Rientjes

Subject: RE: [PATCH v2] mm/slub: Simplify get_partial_node()

On Wed, 13 Mar 2024, Song, Xiongwei wrote:

> > On 2024/3/12 22:05, [email protected] wrote:
> > > From: Xiongwei Song <[email protected]>
> > >
> > > Remove the check of !kmem_cache_has_cpu_partial() because it is always
> > > false, we've known this by calling kmem_cache_debug() before calling
> > > remove_partial(), so we can remove the check.
> > >
> > > Meanwhile, redo filling cpu partial and add comment to improve the
> > > readability.
> > >
> > > Signed-off-by: Xiongwei Song <[email protected]>
> > > ---
> > > Changes in v2:
> > > - Use "#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)" to instead
> > > "if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))" to fix build error.
> > > (Thanks Chengming Zhou)
> > > - Add __maybe_unused for partial_slabs to prevent compiler warning.
> > >
> > > v1:
> > > https://lore.kernel.org/linux-kernel/[email protected]/T/
> > > ---
> > > mm/slub.c | 24 +++++++++++++-----------
> > > 1 file changed, 13 insertions(+), 11 deletions(-)
> > >
> > > diff --git a/mm/slub.c b/mm/slub.c
> > > index a3ab096c38c0..ab526960ee5b 100644
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -2588,7 +2588,7 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> > > {
> > > struct slab *slab, *slab2, *partial = NULL;
> > > unsigned long flags;
> > > - unsigned int partial_slabs = 0;
> > > + unsigned int __maybe_unused partial_slabs = 0;
> > >
> > > /*
> > > * Racy check. If we mistakenly see no partial slabs then we
> > > @@ -2620,19 +2620,21 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> > > if (!partial) {
> > > partial = slab;
> > > stat(s, ALLOC_FROM_PARTIAL);
> > > - } else {
> > > - put_cpu_partial(s, slab, 0);
> > > - stat(s, CPU_PARTIAL_NODE);
> > > - partial_slabs++;
> > > +
> > > + /* Fill cpu partial if needed from next iteration, or break */
> > > + if (IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL))
> > > + continue;
> > > + else
> > > + break;
> > > }
> > > -#ifdef CONFIG_SLUB_CPU_PARTIAL
> > > - if (!kmem_cache_has_cpu_partial(s)
> > > - || partial_slabs > s->cpu_partial_slabs / 2)
> > > +
> > > +#if IS_ENABLED(CONFIG_SLUB_CPU_PARTIAL)
> >
> > Hmm, these two CONFIG_SLUB_CPU_PARTIAL look verbose to me :(
> >
> > How about using just one, maybe like this?
> >
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 2ef88bbf56a3..a018c715b648 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -2620,19 +2620,16 @@ static struct slab *get_partial_node(struct kmem_cache *s,
> > if (!partial) {
> > partial = slab;
> > stat(s, ALLOC_FROM_PARTIAL);
> > +#ifdef CONFIG_SLUB_CPU_PARTIAL
> > } else {
>
> I don't like splitting "if...else..." up with preprocessor directives personally. It's messy for me.
>

I would agree, but the flow here actually seems like it's easier to follow
if we are checking for CONFIG_SLUB_CPU_PARTIAL in multiple places :/