* + mm-percpu-internalh-optimise-pcpu_chunk_struct-to-save-memory.patch added to mm-new branch
@ 2026-03-06 1:47 Andrew Morton
0 siblings, 0 replies; only message in thread
From: Andrew Morton @ 2026-03-06 1:47 UTC (permalink / raw)
To: mm-commits, tj, dennis, cl, zenghongling, akpm
The patch titled
Subject: mm/percpu-internal.h: optimise pcpu_chunk_struct to save memory
has been added to the -mm mm-new branch. Its filename is
mm-percpu-internalh-optimise-pcpu_chunk_struct-to-save-memory.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-percpu-internalh-optimise-pcpu_chunk_struct-to-save-memory.patch
This patch will later appear in the mm-new branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews. Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.
The mm-new branch of mm.git is not included in linux-next
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------------------------------------------------------
From: zenghongling <zenghongling@kylinos.cn>
Subject: mm/percpu-internal.h: optimise pcpu_chunk_struct to save memory
Date: Thu, 5 Mar 2026 15:30:43 +0800
The pcpu_chunk_struct has a hole of 4 bytes and pushes the struct to three
cachelines. Relocating the three booleans upwards allows for the struct
to only use two cachelines.
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_empty_pop_pages; /* 108 4 */
struct obj_cgroup * * obj_cgroups; /* 112 8 */
int nr_pages; /* 120 4 */
int nr_populated; /* 124 4 */
/* --- 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)));
Link: https://lkml.kernel.org/r/20260305073043.571691-1-zenghongling@kylinos.cn
Signed-off-by: zenghongling <zenghongling@kylinos.cn>
Cc: Christoph Lameter <cl@gentwo.org>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Hongling Zeng <zenghongling@kylinos.cn>
Cc: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---
mm/percpu-internal.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/percpu-internal.h~mm-percpu-internalh-optimise-pcpu_chunk_struct-to-save-memory
+++ a/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_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 */
};
_
Patches currently in -mm which might be from zenghongling@kylinos.cn are
mm-percpu-internalh-optimise-pcpu_chunk_struct-to-save-memory.patch
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2026-03-06 1:47 + mm-percpu-internalh-optimise-pcpu_chunk_struct-to-save-memory.patch added to mm-new branch Andrew Morton
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