On Wed, Dec 04, 2019 at 10:53:38AM +0900, Taejoon Song wrote: > The worst-case scenario on finding same element pages is that almost > all elements are same at the first glance but only last few elements > are different. > > Since the same element tends to be grouped from the beginning of the > pages, if we check the first element with the last element before > looping through all elements, we might have some chances to quickly > detect non-same element pages. > > 1. Test is done under LG webOS TV (64-bit arch) > 2. Dump the swap-out pages (~819200 pages) > 3. Analyze the pages with simple test script which counts the iteration > number and measures the speed at off-line > > Under 64-bit arch, the worst iteration count is PAGE_SIZE / 8 bytes = 512. > The speed is based on the time to consume page_same_filled() function only. > The result, on average, is listed as below: > > Num of Iter Speed(MB/s) > Looping-Forward (Orig) 38 99265 > Looping-Backward 36 102725 > Last-element-check (This Patch) 33 125072 > > The result shows that the average iteration count decreases by 13% and > the speed increases by 25% with this patch. This patch does not increase > the overall time complexity, though. > > I also ran simpler version which uses backward loop. Just looping backward > also makes some improvement, but less than this patch. > > Signed-off-by: Taejoon Song <taejoon.song@xxxxxxx> Acked-by: Minchan Kim <minchan@xxxxxxxxxx> I think it's very reasonable optimization with small cost.
