From: zenghongling <zenghongling@kylinos.cn>
To: dennis@kernel.org, tj@kernel.org, cl@gentwo.org,
akpm@linux-foundation.org
Cc: linux-mm@kvack.org, kernel@vger.kernel.org,
zhongling0719@126.com, zenghongling <zenghongling@kylinos.cn>
Subject: [PATCH v2] mm/percpu-internal.h: optimise pcpu_chunk struct to save memory
Date: Thu, 9 Apr 2026 10:30:10 +0800 [thread overview]
Message-ID: <20260409023010.10493-1-zenghongling@kylinos.cn> (raw)
Using pahole, we can see that there are some padding holes
in the current pcpu_chunk structure,Adjusting the layout of pcpu_chunk
can reduce these holes,decreasing its size from 192 bytes to 128 bytes
and eliminating a wasted cache line.
With allmodconfig (CONFIG_PERCPU_STATS + NEED_PCPUOBJ_EXT)
Before:
/* size: 256, cachelines: 4, members: 19 */
After:
/* size: 192, cachelines: 3, members: 19 */
with NEED_PCPUOBJ_EXT
Before:
struct pcpu_chunk {
struct list_head list; /* 0 16 */
int free_bytes; /* 16 4 */
struct pcpu_block_md chunk_md; /* 20 32 */
/* XXX 4 bytes hole, try to pack */
long unsigned int * bound_map; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
void * base_addr __attribute__((__aligned__(64))); /* 64 8 */
long unsigned int * alloc_map; /* 72 8 */
struct pcpu_block_md * md_blocks; /* 80 8 */
void * data; /* 88 8 */
bool immutable; /* 96 1 */
bool isolated; /* 97 1 */
/* XXX 2 bytes hole, try to pack */
int start_offset; /* 100 4 */
int end_offset; /* 104 4 */
/* XXX 4 bytes hole, try to pack */
struct obj_cgroup * * obj_cgroups; /* 112 8 */
int nr_pages; /* 120 4 */
int nr_populated; /* 124 4 */
/* --- cacheline 2 boundary (128 bytes) --- */
int nr_empty_pop_pages; /* 128 4 */
/* XXX 4 bytes hole, try to pack */
long unsigned int populated[]; /* 136 0 */
/* size: 192, cachelines: 3, members: 17 */
/* sum members: 122, holes: 4, sum holes: 14 */
/* padding: 56 */
/* forced alignments: 1 */
} __attribute__((__aligned__(64)));
After:
struct pcpu_chunk {
struct list_head list; /* 0 16 */
int free_bytes; /* 16 4 */
struct pcpu_block_md chunk_md; /* 20 32 */
/* XXX 4 bytes hole, try to pack */
long unsigned int * bound_map; /* 56 8 */
/* --- cacheline 1 boundary (64 bytes) --- */
void * base_addr __attribute__((__aligned__(64))); /* 64 8 */
long unsigned int * alloc_map; /* 72 8 */
struct pcpu_block_md * md_blocks; /* 80 8 */
void * data; /* 88 8 */
bool immutable; /* 96 1 */
bool isolated; /* 97 1 */
/* XXX 2 bytes hole, try to pack */
int start_offset; /* 100 4 */
int end_offset; /* 104 4 */
int nr_pages; /* 108 4 */
int nr_populated; /* 112 4 */
int nr_empty_pop_pages; /* 116 4 */
struct obj_cgroup * * obj_cgroups; /* 120 8 */
/* --- cacheline 2 boundary (128 bytes) --- */
long unsigned int populated[]; /* 128 0 */
/* size: 128, cachelines: 2, members: 17 */
/* sum members: 122, holes: 2, sum holes: 6 */
/* forced alignments: 1 */
} __attribute__((__aligned__(64)));
Suggested-by: Dennis Zhou <dennis@kernel.org>
Signed-off-by: zenghongling <zenghongling@kylinos.cn>
---
Changes in v2:
- Add pahole output for allmodconfig (CONFIG_PERCPU_STATS + NEED_PCPUOBJ_EXT)
- Fix subject to use "pcpu_chuck struct"
- Reorder nr_pages before nr_empty_pop_pages
- Add suggest by
Changes in v1:
- Fix the error commit message.
- Move nr_pages over nr_empty_pop_pages.
---
---
mm/percpu-internal.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/mm/percpu-internal.h b/mm/percpu-internal.h
index 4b3d6ec43703..8cbe039bf847 100644
--- a/mm/percpu-internal.h
+++ b/mm/percpu-internal.h
@@ -77,13 +77,13 @@ struct pcpu_chunk {
int end_offset; /* additional area required to
have the region end page
aligned */
+ int nr_pages; /* # of pages served by this chunk */
+ int nr_populated; /* # of populated pages */
+ int nr_empty_pop_pages; /* # of empty populated pages */
#ifdef NEED_PCPUOBJ_EXT
struct pcpuobj_ext *obj_exts; /* vector of object cgroups */
#endif
- int nr_pages; /* # of pages served by this chunk */
- int nr_populated; /* # of populated pages */
- int nr_empty_pop_pages; /* # of empty populated pages */
unsigned long populated[]; /* populated bitmap */
};
--
2.25.1
next reply other threads:[~2026-04-09 2:30 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-09 2:30 zenghongling [this message]
-- strict thread matches above, loose matches on Subject: below --
2026-04-09 2:25 zenghongling
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260409023010.10493-1-zenghongling@kylinos.cn \
--to=zenghongling@kylinos.cn \
--cc=akpm@linux-foundation.org \
--cc=cl@gentwo.org \
--cc=dennis@kernel.org \
--cc=kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=tj@kernel.org \
--cc=zhongling0719@126.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox