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Mempool c->fill_iter is used to allocate memory for struct btree_iter in bch_btree_node_read_done() to iterate all keys of a read-in btree node. The allocation size is defined in bch_cache_set_alloc() by, mempool_init_kmalloc_pool(&c->fill_iter, 1, iter_size)) where iter_size is defined by a calculation, (sb->bucket_size / sb->block_size + 1) * sizeof(struct btree_iter_set) For 16bit width bucket_size the calculation is OK, but now the bucket size is extended to 32bit, the bucket size can be 2GB. By the above calculation, iter_size can be 2048 pages (order 11 is still accepted by buddy allocator). But the actual size holds the bkeys in meta data bucket is limited to meta_bucket_pages() already, which is 16MB. By the above calculation, if replace sb->bucket_size by meta_bucket_pages() * PAGE_SECTORS, the result is 16 pages. This is the size large enough for the mempool allocation to struct btree_iter. Therefore in worst case every time mempool c->fill_iter allocates, at most 4080 pages are wasted and won't be used. Therefore this patch uses meta_bucket_pages() * PAGE_SECTORS to calculate the iter size in bch_cache_set_alloc(), to avoid extra memory allocation from mempool c->fill_iter. Signed-off-by: Coly Li <colyli@suse.de> Reviewed-by: Hannes Reinecke <hare@suse.de> Signed-off-by: Jens Axboe <axboe@kernel.dk>
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 Restructured Text 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.