From: "Kirill A. Shutemov" <kirill@xxxxxxxxxxxxx> Date: Mon, 3 Nov 2014 23:52:06 +0200 > On Mon, Nov 03, 2014 at 04:36:28PM -0500, Johannes Weiner wrote: >> On Mon, Nov 03, 2014 at 11:06:07PM +0200, Kirill A. Shutemov wrote: >> > On Sat, Nov 01, 2014 at 11:15:54PM -0400, Johannes Weiner wrote: >> > > Memory cgroups used to have 5 per-page pointers. To allow users to >> > > disable that amount of overhead during runtime, those pointers were >> > > allocated in a separate array, with a translation layer between them >> > > and struct page. >> > > >> > > There is now only one page pointer remaining: the memcg pointer, that >> > > indicates which cgroup the page is associated with when charged. The >> > > complexity of runtime allocation and the runtime translation overhead >> > > is no longer justified to save that *potential* 0.19% of memory. >> > >> > How much do you win by the change? >> >> Heh, that would have followed right after where you cut the quote: >> with CONFIG_SLUB, that pointer actually sits in already existing >> struct page padding, which means that I'm saving one pointer per page >> (8 bytes per 4096 byte page, 0.19% of memory), plus the pointer and >> padding in each memory section. I also save the (minor) translation >> overhead going from page to page_cgroup and the maintenance burden >> that stems from having these auxiliary arrays (see deleted code). > > I read the description. I want to know if runtime win (any benchmark data?) > from moving mem_cgroup back to the struct page is measurable. > > If the win is not significant, I would prefer to not occupy the padding: > I'm sure we will be able to find a better use for the space in struct page > in the future. I think the simplification benefits completely trump any performan metric. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>