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When handing slab objects, we use obj_cgroup_[un]charge() for (un)charging and mod_objcg_state() to account NR_SLAB_[UN]RECLAIMABLE_B. All these operations use the percpu stock for performance. However with the calls being separate, the stock_lock is taken twice in each case. By refactoring the code, we can turn mod_objcg_state() into __account_obj_stock() which is called on a stock that's already locked and validated. On the charging side we can call this function from consume_obj_stock() when it succeeds, and refill_obj_stock() in the fallback. We just expand parameters of these functions as necessary. The uncharge side from __memcg_slab_free_hook() is just the call to refill_obj_stock(). Other callers of obj_cgroup_[un]charge() (i.e. not slab) simply pass the extra parameters as NULL/zeroes to skip the __account_obj_stock() operation. In __memcg_slab_post_alloc_hook() we now charge each object separately, but that's not a problem as we did call mod_objcg_state() for each object separately, and most allocations are non-bulk anyway. This could be improved by batching all operations until slab_pgdat(slab) changes. Some preliminary benchmarking with a kfree(kmalloc()) loop of 10M iterations with/without __GFP_ACCOUNT: Before the patch: kmalloc/kfree !memcg: 581390144 cycles kmalloc/kfree memcg: 783689984 cycles After the patch: kmalloc/kfree memcg: 658723808 cycles More than half of the overhead of __GFP_ACCOUNT relative to non-accounted case seems eliminated. Link: https://lkml.kernel.org/r/20250404013913.1663035-9-shakeel.butt@linux.dev Signed-off-by: Shakeel Butt <shakeel.butt@linux.dev> Signed-off-by: Vlastimil Babka <vbabka@suse.cz> Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@kernel.org> Cc: Muchun Song <muchun.song@linux.dev> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> 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.