On Fri, 6 Sep 2013, Joonsoo Kim wrote: > Currently, the freelist of a slab consist of unsigned int sized indexes. > Most of slabs have less number of objects than 256, since restriction > for page order is at most 1 in default configuration. For example, > consider a slab consisting of 32 byte sized objects on two continous > pages. In this case, 256 objects is possible and these number fit to byte > sized indexes. 256 objects is maximum possible value in default > configuration, since 32 byte is minimum object size in the SLAB. > (8192 / 32 = 256). Therefore, if we use byte sized index, we can save > 3 bytes for each object.
Ok then why is the patch making slab do either byte sized or int sized indexes? Seems that you could do a clean cutover? As you said: The mininum object size is 32 bytes for slab. 32 * 256 = 8k. So we are fine unless the page size is > 8k. This is true for IA64 and powerpc only I believe. The page size can be determined at compile time and depending on that page size you could then choose a different size for the indexes. Or the alternative is to increase the minimum slab object size. A 16k page size would require a 64 byte minimum allocation. But thats no good I guess. byte sized or short int sized index support would be enough. > This introduce one likely branch to functions used for setting/getting > objects to/from the freelist, but we may get more benefits from > this change. Lets not do that. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
