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Message-ID: <ZLstfVZZUJigJzNq@MiWiFi-R3L-srv>
Date: Sat, 22 Jul 2023 09:14:37 +0800
From: Baoquan He <bhe@...hat.com>
To: Dennis Zhou <dennis@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
akpm@...ux-foundation.org, tj@...nel.org, cl@...ux.com,
mawupeng1@...wei.com
Subject: Re: [PATCH 2/3] mm/percpu.c: optimize the code in
pcpu_setup_first_chunk() a little bit
On 07/21/23 at 02:01pm, Dennis Zhou wrote:
> Hello,
>
> On Fri, Jul 21, 2023 at 09:17:59PM +0800, Baoquan He wrote:
> > This removes the need of local varibale 'chunk', and optimize the code
> > calling pcpu_alloc_first_chunk() to initialize reserved chunk and
> > dynamic chunk to make it simpler.
> >
> > Signed-off-by: Baoquan He <bhe@...hat.com>
> > ---
> > mm/percpu.c | 32 +++++++++++++-------------------
> > 1 file changed, 13 insertions(+), 19 deletions(-)
> >
> > diff --git a/mm/percpu.c b/mm/percpu.c
> > index 1480bf283d11..c25b058a46ad 100644
> > --- a/mm/percpu.c
> > +++ b/mm/percpu.c
> > @@ -2581,7 +2581,6 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
> > {
> > size_t size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;
> > size_t static_size, dyn_size;
> > - struct pcpu_chunk *chunk;
> > unsigned long *group_offsets;
> > size_t *group_sizes;
> > unsigned long *unit_off;
> > @@ -2697,7 +2696,7 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
> > pcpu_unit_pages = ai->unit_size >> PAGE_SHIFT;
> > pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;
> > pcpu_atom_size = ai->atom_size;
> > - pcpu_chunk_struct_size = struct_size(chunk, populated,
> > + pcpu_chunk_struct_size = struct_size((struct pcpu_chunk *)0, populated,
> > BITS_TO_LONGS(pcpu_unit_pages));
> >
> > pcpu_stats_save_ai(ai);
> > @@ -2735,28 +2734,23 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
> >
> > /*
> > * Initialize first chunk.
> > - * If the reserved_size is non-zero, this initializes the reserved
> > - * chunk. If the reserved_size is zero, the reserved chunk is NULL
> > - * and the dynamic region is initialized here. The first chunk,
> > - * pcpu_first_chunk, will always point to the chunk that serves
> > - * the dynamic region.
> > + * If the reserved_size is non-zero, initializes the reserved chunk
> ^initialize
> > + * firstly. If the reserved_size is zero, the reserved chunk is NULL
> ^ can remove firstly.
> > + * and the dynamic region is initialized directly. The first chunk,
> > + * pcpu_first_chunk, will always point to the chunk that serves the
> > + * dynamic region.
>
> Reading this, I'll probably reword this comment to explain the reserved
> chunk better.
Agree. The expression is a little messy and too colloquial.
>
> > */
> > tmp_addr = (unsigned long)base_addr + static_size;
> > - map_size = ai->reserved_size ?: dyn_size;
> > - chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
> > -
> > - /* init dynamic chunk if necessary */
> > if (ai->reserved_size) {
> > - pcpu_reserved_chunk = chunk;
> > -
> > - tmp_addr = (unsigned long)base_addr + static_size +
> > - ai->reserved_size;
> > - map_size = dyn_size;
> > - chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
> > + map_size = ai->reserved_size;
> > + pcpu_reserved_chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
> > }
> >
> > - /* link the first chunk in */
> > - pcpu_first_chunk = chunk;
> > + /* init dynamic chunk if necessary */
> > + tmp_addr += (unsigned long)ai->reserved_size;
>
> I'm not a big fan of += the tmp_addr as I personally find it easier to
> read if it's just laid out explicitly.
OK, will change.
>
> > + map_size = dyn_size;
> > + pcpu_first_chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
> > +
> > pcpu_nr_empty_pop_pages = pcpu_first_chunk->nr_empty_pop_pages;
> > pcpu_chunk_relocate(pcpu_first_chunk, -1);
> >
> > --
> > 2.34.1
> >
>
> Overall, I think this is good, but I'd go 1 step further and get rid of
> map_size. Regarding tmp_addr, I'd prefer if we kept all the math
> together.
Makes sense. Thanks a lot for your careful review and great suggestions.
According to your comments, I made a draft v2. Please help check if I
have got them correctly and if the new change is OK to you.
>From 17832ce8a755d8327b853a18c6f1cc00c9f93e50 Mon Sep 17 00:00:00 2001
From: Baoquan He <bhe@...hat.com>
Date: Tue, 27 Jun 2023 09:33:28 +0800
Subject: [PATCH] mm/percpu.c: optimize the code in pcpu_setup_first_chunk() a
little bit
Content-type: text/plain
This removes the need of local varibale 'chunk', and optimize the code
calling pcpu_alloc_first_chunk() to initialize reserved chunk and
dynamic chunk to make it simpler.
Signed-off-by: Baoquan He <bhe@...hat.com>
---
mm/percpu.c | 36 +++++++++++++-----------------------
1 file changed, 13 insertions(+), 23 deletions(-)
diff --git a/mm/percpu.c b/mm/percpu.c
index 1480bf283d11..83fc47206680 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -2581,14 +2581,12 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
{
size_t size_sum = ai->static_size + ai->reserved_size + ai->dyn_size;
size_t static_size, dyn_size;
- struct pcpu_chunk *chunk;
unsigned long *group_offsets;
size_t *group_sizes;
unsigned long *unit_off;
unsigned int cpu;
int *unit_map;
int group, unit, i;
- int map_size;
unsigned long tmp_addr;
size_t alloc_size;
@@ -2697,7 +2695,7 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
pcpu_unit_pages = ai->unit_size >> PAGE_SHIFT;
pcpu_unit_size = pcpu_unit_pages << PAGE_SHIFT;
pcpu_atom_size = ai->atom_size;
- pcpu_chunk_struct_size = struct_size(chunk, populated,
+ pcpu_chunk_struct_size = struct_size((struct pcpu_chunk *)0, populated,
BITS_TO_LONGS(pcpu_unit_pages));
pcpu_stats_save_ai(ai);
@@ -2734,29 +2732,21 @@ void __init pcpu_setup_first_chunk(const struct pcpu_alloc_info *ai,
dyn_size = ai->dyn_size - (static_size - ai->static_size);
/*
- * Initialize first chunk.
- * If the reserved_size is non-zero, this initializes the reserved
- * chunk. If the reserved_size is zero, the reserved chunk is NULL
- * and the dynamic region is initialized here. The first chunk,
- * pcpu_first_chunk, will always point to the chunk that serves
- * the dynamic region.
+ * Initialize first chunk:
+ *
+ * - If the reserved_size is non-zero, initialize the reserved
+ * chunk firstly. Otherwise, the reserved chunk is NULL.
+ *
+ * - The first chunk, pcpu_first_chunk, always points to the
+ * chunk that serves the dynamic region.
*/
tmp_addr = (unsigned long)base_addr + static_size;
- map_size = ai->reserved_size ?: dyn_size;
- chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
-
- /* init dynamic chunk if necessary */
- if (ai->reserved_size) {
- pcpu_reserved_chunk = chunk;
-
- tmp_addr = (unsigned long)base_addr + static_size +
- ai->reserved_size;
- map_size = dyn_size;
- chunk = pcpu_alloc_first_chunk(tmp_addr, map_size);
- }
+ if (ai->reserved_size)
+ pcpu_reserved_chunk = pcpu_alloc_first_chunk(tmp_addr,
+ ai->reserved_size);
+ tmp_addr = (unsigned long)base_addr + static_size + ai->reserved_size;
+ pcpu_first_chunk = pcpu_alloc_first_chunk(tmp_addr, dyn_size);
- /* link the first chunk in */
- pcpu_first_chunk = chunk;
pcpu_nr_empty_pop_pages = pcpu_first_chunk->nr_empty_pop_pages;
pcpu_chunk_relocate(pcpu_first_chunk, -1);
--
2.34.1
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