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1b6a58e205
When tracing mem_cgroup_per_node allocations with kmalloc ftrace:
kmalloc: call_site=mem_cgroup_css_alloc+0x1d8/0x5b4 ptr=00000000d798700c
bytes_req=2896 bytes_alloc=4096 gfp_flags=GFP_KERNEL|__GFP_ZERO node=0
accounted=false
This reveals the slab allocator provides 4096B chunks for 2896B
mem_cgroup_per_node due to:
1. The slab allocator predefines bucket sizes from 64B to 8096B
2. The mem_cgroup allocation size (2312B) falls between the 2KB and 4KB
slabs
3. The allocator rounds up to the nearest larger slab (4KB), resulting in
~1KB wasted memory per memcg alloc - per node.
This patch introduces a dedicated kmem_cache for mem_cgroup structs,
achieving precise memory allocation. Post-patch ftrace verification shows:
kmem_cache_alloc: call_site=mem_cgroup_css_alloc+0x1b8/0x5d4
ptr=000000002989e63a bytes_req=2896 bytes_alloc=2944
gfp_flags=GFP_KERNEL|__GFP_ZERO node=0 accounted=false
Each mem_cgroup_per_node alloc 2944bytes(include hw cacheline align),
compare to 4096, it avoid waste.
Link: https://lkml.kernel.org/r/20250425031935.76411-4-link@vivo.com
Signed-off-by: Huan Yang <link@vivo.com>
Acked-by: Shakeel Butt <shakeel.butt@linux.dev>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: Francesco Valla <francesco@valla.it>
Cc: guoweikang <guoweikang.kernel@gmail.com>
Cc: Huang Shijie <shijie@os.amperecomputing.com>
Cc: KP Singh <kpsingh@kernel.org>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: "Paul E . McKenney" <paulmck@kernel.org>
Cc: Petr Mladek <pmladek@suse.com>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Raul E Rangel <rrangel@chromium.org>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.