Re: [PATCH -mm -v10 2/3] mm, THP, swap: Check whether THP can be split firstly

[Johannes Weiner]

On Tue, Apr 25, 2017 at 08:56:57PM +0800, Huang, Ying wrote:
> From: Huang Ying <ying.huang@xxxxxxxxx>
> 
> To swap out THP (Transparent Huage Page), before splitting the THP,
> the swap cluster will be allocated and the THP will be added into the
> swap cache.  But it is possible that the THP cannot be split, so that
> we must delete the THP from the swap cache and free the swap cluster.
> To avoid that, in this patch, whether the THP can be split is checked
> firstly.  The check can only be done racy, but it is good enough for
> most cases.
> 
> With the patch, the swap out throughput improves 3.6% (from about
> 4.16GB/s to about 4.31GB/s) in the vm-scalability swap-w-seq test case
> with 8 processes.  The test is done on a Xeon E5 v3 system.  The swap
> device used is a RAM simulated PMEM (persistent memory) device.  To
> test the sequential swapping out, the test case creates 8 processes,
> which sequentially allocate and write to the anonymous pages until the
> RAM and part of the swap device is used up.
> 
> Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
> Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
> Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> [for can_split_huge_page()]

Acked-by: Johannes Weiner <hannes@xxxxxxxxxxx>