Messages in this thread Patch in this message | | | Date | Fri, 6 May 2016 12:25:18 +0800 | Subject | Re: [PATCH] mm/zsmalloc: avoid unnecessary iteration in get_pages_per_zspage() | From | Ganesh Mahendran <> |
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Hi, Minchan:
2016-05-06 11:09 GMT+08:00 Minchan Kim <minchan@kernel.org>: > On Thu, May 05, 2016 at 07:03:29PM +0900, Sergey Senozhatsky wrote: >> On (05/05/16 13:17), Ganesh Mahendran wrote: >> > if we find a zspage with usage == 100%, there is no need to >> > try other zspages. >> >> Hello, >> >> well... we iterate there from 0 to 1<<2, which is not awfully >> a lot to break it in the middle, and we do this only when we >> initialize a new pool (for every size class). >> >> the check is >> - true 15 times >> - false 492 times > > Thanks for the data, Sergey! > >> >> so it _sort of_ feels like this new if-condition doesn't >> buy us a lot, and most of the time it just sits there with >> no particular gain. let's hear from Minchan. >> > > I agree with Sergey. > First of al, I appreciates your patch, Ganesh! But as Sergey pointed > out, I don't see why it improves current zsmalloc.
This patch does not obviously improve zsmalloc. It just reduces unnecessary code path.
From data provided by Sergey, 15 * (4 - 1) = 45 times loop will be avoided. So 45 times of below caculation will be reduced: --- zspage_size = i * PAGE_SIZE; waste = zspage_size % class_size; usedpc = (zspage_size - waste) * 100 / zspage_size;
if (usedpc > max_usedpc) { ---
Thanks.
> If you want to merge strongly, please convince me with more detail > reason. > > Thanks. > > >> -ss >> >> > Signed-off-by: Ganesh Mahendran <opensource.ganesh@gmail.com> >> > Cc: Minchan Kim <minchan@kernel.org> >> > Cc: Nitin Gupta <ngupta@vflare.org> >> > Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> >> > --- >> > mm/zsmalloc.c | 3 +++ >> > 1 file changed, 3 insertions(+) >> > >> > diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c >> > index fda7177..310c7b0 100644 >> > --- a/mm/zsmalloc.c >> > +++ b/mm/zsmalloc.c >> > @@ -765,6 +765,9 @@ static int get_pages_per_zspage(int class_size) >> > if (usedpc > max_usedpc) { >> > max_usedpc = usedpc; >> > max_usedpc_order = i; >> > + >> > + if (max_usedpc == 100) >> > + break; >> > } >> > } >> > >> > -- >> > 1.7.9.5 >> >
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