• Aneesh Kumar K.V's avatar
    powerpc/mm/radix: Update pte fragment count from 16 to 256 on radix · fb4e5dbd
    Aneesh Kumar K.V authored
    With split PTL (page table lock) config, we allocate the level
    4 (leaf) page table using pte fragment framework instead of slab cache
    like other levels. This was done to enable us to have split page table
    lock at the level 4 of the page table. We use page->plt backing the
    all the level 4 pte fragment for the lock.
    
    Currently with Radix, we use only 16 fragments out of the allocated
    page. In radix each fragment is 256 bytes which means we use only 4k
    out of the allocated 64K page wasting 60k of the allocated memory.
    This was done earlier to keep it closer to hash.
    
    This patch update the pte fragment count to 256, thereby using the
    full 64K page and reducing the memory usage. Performance tests shows
    really low impact even with THP disabled. With THP disabled we will be
    contenting further less on level 4 ptl and hence the impact should be
    further low.
    
      256 threads:
        without patch (10 runs of ./ebizzy  -m -n 1000 -s 131072 -S 100)
          median = 15678.5
          stdev = 42.1209
    
        with patch:
          median = 15354
          stdev = 194.743
    
    This is with THP disabled. With THP enabled the impact of the patch
    will be less.
    Signed-off-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
    fb4e5dbd
radix-4k.h 556 Bytes