On 4/14/21 4:38 AM, lipeifeng@xxxxxxxx wrote: > From: lipeifeng <lipeifeng@xxxxxxxx> > > This patch would "sort" the free-pages in buddy by pages-PFN to concentrate > low-order-pages allocation in the front area of memory and high-order-pages > allcation on the contrary so that few memory-pollution in the back area of > memory and the probablity of high-order-pages allocation would be increased > significantly. > ----------------------------------------------------------------------- > > 1) Divide memory into several segments by pages-PFN > "Multi_freearea" would divide memory into FREE_AREA_COUNTS segments > by pages-PFN,each memory-segment corresponds to a free_area. > > Example: machine(4G of physical memery) and FREE_AREA_COUNTS(4): > page-PFN:0x0 0x40000(1G) 0x80000(2G) 0xc0000(3G) 0xFFFFF(4G) > |------------|--------------|--------------|-------------| > free_area: [0][] [1][] [2][] [3][] > > NOTE: Selecting the corresponding freearea when pages are freed back > to buddy: > - pages-PFN[0, free_area_segment[0].max_pfn] -> free_area[0][] > - pages-PFN[free_area_segment[flc - 1].max_pfn, > free_area_segment[flc].max_pfn] -> free_area[flc][] > (flc > 0) > > By this way, all pages in the same segment/free_area is within a > certain range of pages-PFN. > > 2) Select the corresponding freearea to alloc-pages > "Multi_freearea" would select the corresponding free_area by the > allocation-order when alloc-pages. > - order < HIGH_ORDER_TO_FLC: > free_area[0] -> ... -> free_area[FREE_AREA_COUNTS - 1] > - order >= HIGH_ORDER_TO_FLC: > free_area[FREE_AREA_COUNTS - 1] -> ... -> free_area[0] > > Example: > The machine(4G of physical memery) and FREE_AREA_COUNTS(4) > and HIGH_ORDER_TO_FLC(3). > If user allocs page(order = 0),it would take page from > free_area[0][] first, if that fails,try free_area[1][] and so on. > If user allocs page(order = 4),it would take page from > free_area[3][] first, if that fails,try free_area[2][] and so on. > > By this way,low-order pages will be concentrated in the front area > of memory.Because of few memory-pollution in the back area of memory, > the sussessful probablity of high-order allocation would be improved. > > 3) Adjust the location of free-pages in the free_list > "Multi_freearea" would place free-pages in the head of free_list if > pages-PFN is smaller than free_area_segment[flc]->median_pfn and in > the tail of free_list on the contrary. > > Example: > page-PFN: free_area_segment[flc]->median_pfn > | > free_list: page->page->page->...|...page->page->page > pages-PFN:| < median_pfn | >= median_pfn | > > Because it would take pages from the head of the freelist first in > buddy system,the free-pages in the tail are more likely to keep in the > buddy system.The closer the PFN of pages kept in buddy system, the > greater the probablity of merging that into high-order pages. I think this part 3) would be worth to be tried separately first, as it's not a big change compared to the other ones.
