On 10/18/2017 09:59 AM, Mel Gorman wrote: > As the page free path makes no distinction between cache hot and cold > pages, there is no real useful ordering of pages in the free list that > allocation requests can take advantage of. Juding from the users of > __GFP_COLD, it is likely that a number of them are the result of copying > other sites instead of actually measuring the impact. Remove the > __GFP_COLD parameter which simplifies a number of paths in the page > allocator. > > This is potentially controversial but bear in mind that the size of the > per-cpu pagelists versus modern cache sizes means that the whole per-cpu > list can often fit in the L3 cache. Hence, there is only a potential benefit > for microbenchmarks that alloc/free pages in a tight loop. It's even worse > when THP is taken into account which has little or no chance of getting a > cache-hot page as the per-cpu list is bypassed and the zeroing of multiple > pages will thrash the cache anyway. > > The truncate microbenchmarks are not shown as this patch affects the > allocation path and not the free path. A page fault microbenchmark was > tested but it showed no sigificant difference which is not surprising given > that the __GFP_COLD branches are a miniscule percentage of the fault path. > > Signed-off-by: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
