On Thu, 24 May 2012 14:52:26 -0700 (PDT) David Rientjes <rientjes@xxxxxxxxxx> wrote: > On Mon, 16 Apr 2012, Aneesh Kumar K.V wrote: > > > This patch implements a memcg extension that allows us to control HugeTLB > > allocations via memory controller. The extension allows to limit the > > HugeTLB usage per control group and enforces the controller limit during > > page fault. Since HugeTLB doesn't support page reclaim, enforcing the limit > > at page fault time implies that, the application will get SIGBUS signal if it > > tries to access HugeTLB pages beyond its limit. This requires the application > > to know beforehand how much HugeTLB pages it would require for its use. > > > > The charge/uncharge calls will be added to HugeTLB code in later patch. > > Support for memcg removal will be added in later patches. > > > > Again, I disagree with this approach because it's adding the functionality > to memcg when it's unnecessary; it would be a complete legitimate usecase > to want to limit the number of globally available hugepages to a set of > tasks without incurring the per-page tracking from memcg. > > This can be implemented as a seperate cgroup and as we move to a single > hierarchy, you lose no functionality if you mount both cgroups from what > is done here. > > It would be much cleaner in terms of > > - build: not requiring ifdefs and dependencies on CONFIG_HUGETLB_PAGE, > which is a prerequisite for this functionality and is not for > CONFIG_CGROUP_MEM_RES_CTLR, > > - code: seperating hugetlb bits out from memcg bits to avoid growing > mm/memcontrol.c beyond its current 5650 lines, and > > - performance: not incurring any overhead of enabling memcg for per- > page tracking that is unnecessary if users only want to limit hugetlb > pages. > > Kmem accounting and swap accounting is really a seperate topic and makes > sense to be incorporated directly into memcg because their usage is a > single number, the same is not true for hugetlb pages where charging one > 1GB page is not the same as charging 512 2M pages. And we have no > usecases for wanting to track kmem or swap only without user page > tracking, what would be the point? > > There's a reason we don't enable CONFIG_CGROUP_MEM_RES_CTLR in the > defconfig, we don't want the extra 1% metadata overhead of enabling it and > the potential performance regression from doing per-page tracking if we > only want to limit a global resource (hugetlb pages) to a set of tasks. > > So please consider seperating this functionality out into its own cgroup, > there's no reason not to do it and it would benefit hugetlb users who > don't want to incur the disadvantages of enabling memcg entirely. These arguments look pretty strong to me. But poorly timed :( -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>