Andrew Morton <a...@linux-foundation.org> writes: > On Thu, 1 Sep 2016 08:16:54 -0700 "Huang, Ying" <ying.hu...@intel.com> wrote: > >> From: Huang Ying <ying.hu...@intel.com> >> >> In this patch, the size of the swap cluster is changed to that of the >> THP (Transparent Huge Page) on x86_64 architecture (512). This is for >> the THP swap support on x86_64. Where one swap cluster will be used to >> hold the contents of each THP swapped out. And some information of the >> swapped out THP (such as compound map count) will be recorded in the >> swap_cluster_info data structure. >> >> In effect, this will enlarge swap cluster size by 2 times. Which may >> make it harder to find a free cluster when the swap space becomes >> fragmented. So that, this may reduce the continuous swap space >> allocation and sequential write in theory. The performance test in 0day >> show no regressions caused by this. >> >> --- a/mm/swapfile.c >> +++ b/mm/swapfile.c >> @@ -196,7 +196,7 @@ static void discard_swap_cluster(struct swap_info_struct >> *si, >> } >> } >> >> -#define SWAPFILE_CLUSTER 256 >> +#define SWAPFILE_CLUSTER 512 >> #define LATENCY_LIMIT 256 >> > > What happens to architectures which have different HPAGE_SIZE and/or > PAGE_SIZE?
For the architecture with HPAGE_SIZE / PAGE_SIZE == 512 (for example x86_64), the huge page swap optimizing will be turned on. For other architectures, it will be turned off as before. This mostly because I don't know whether it is a good idea to turn on THP swap optimizing for the architectures other than x86_64. For example, it appears that the huge page size is 8M (1<<23) on SPARC. But I don't know whether 8M is too big for a swap cluster. And it appears that the huge page size could be as large as 512M on MIPS. Best Regards, Huang, Ying
