Benjamin Herrenschmidt <b...@kernel.crashing.org> writes: > On Mon, 2015-09-21 at 12:10 +0530, Aneesh Kumar K.V wrote: >> /* >> - * We use a 2K PTE page fragment and another 2K for storing >> - * real_pte_t hash index >> + * We use a 2K PTE page fragment and another 4K for storing >> + * real_pte_t hash index. Rounding the entire thing to 8K >> */ > > Isn't this a LOT of memory wasted ? Page tables have a non-negligible > footprint, we were already wasting half, now we are wasting 3/4 no ? >
The actual math is, we used to allocate 16 PTE page from a 64K page before. We now do 8 pte page from a 64K linux page. > Ie, in most cases on modern machines we never use the other "half"... > That is true. We will use this only when we use 4K subpage. But I am not sure there is a better solution. Also, we should find this slightly imporve our contention on ptl lock. With SPLIT_PTLOCK we now have less number of pte page using the same spin lock. -aneesh _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
