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3c1ea5c501
Add functions for efficient guaranteed allocations e.g. in a critical section that cannot sleep, when the exact number of allocations is not known beforehand, but an upper limit can be calculated. kmem_cache_prefill_sheaf() returns a sheaf containing at least given number of objects. kmem_cache_alloc_from_sheaf() will allocate an object from the sheaf and is guaranteed not to fail until depleted. kmem_cache_return_sheaf() is for giving the sheaf back to the slab allocator after the critical section. This will also attempt to refill it to cache's sheaf capacity for better efficiency of sheaves handling, but it's not stricly necessary to succeed. kmem_cache_refill_sheaf() can be used to refill a previously obtained sheaf to requested size. If the current size is sufficient, it does nothing. If the requested size exceeds cache's sheaf_capacity and the sheaf's current capacity, the sheaf will be replaced with a new one, hence the indirect pointer parameter. kmem_cache_sheaf_size() can be used to query the current size. The implementation supports requesting sizes that exceed cache's sheaf_capacity, but it is not efficient - such "oversize" sheaves are allocated fresh in kmem_cache_prefill_sheaf() and flushed and freed immediately by kmem_cache_return_sheaf(). kmem_cache_refill_sheaf() might be especially ineffective when replacing a sheaf with a new one of a larger capacity. It is therefore better to size cache's sheaf_capacity accordingly to make oversize sheaves exceptional. CONFIG_SLUB_STATS counters are added for sheaf prefill and return operations. A prefill or return is considered _fast when it is able to grab or return a percpu spare sheaf (even if the sheaf needs a refill to satisfy the request, as those should amortize over time), and _slow otherwise (when the barn or even sheaf allocation/freeing has to be involved). sheaf_prefill_oversize is provided to determine how many prefills were oversize (counter for oversize returns is not necessary as all oversize refills result in oversize returns). When slub_debug is enabled for a cache with sheaves, no percpu sheaves exist for it, but the prefill functionality is still provided simply by all prefilled sheaves becoming oversize. If percpu sheaves are not created for a cache due to not passing the sheaf_capacity argument on cache creation, the prefills also work through oversize sheaves, but there's a WARN_ON_ONCE() to indicate the omission. Reviewed-by: Suren Baghdasaryan <surenb@google.com> Reviewed-by: Harry Yoo <harry.yoo@oracle.com> Signed-off-by: Vlastimil Babka <vbabka@suse.cz> |
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