On Tue, Feb 22, 2011 at 06:06:30PM -0500, Vivek Goyal wrote: > On Wed, Feb 23, 2011 at 12:01:47AM +0100, Andrea Righi wrote: > > On Tue, Feb 22, 2011 at 01:01:45PM -0700, Jonathan Corbet wrote: > > > On Tue, 22 Feb 2011 18:12:54 +0100 > > > Andrea Righi <arighi@xxxxxxxxxxx> wrote: > > > > > > > The page_cgroup infrastructure, currently available only for the memory > > > > cgroup controller, can be used to store the owner of each page and > > > > opportunely track the writeback IO. This information is encoded in > > > > the upper 16-bits of the page_cgroup->flags. > > > > > > > > A owner can be identified using a generic ID number and the following > > > > interfaces are provided to store a retrieve this information: > > > > > > > > unsigned long page_cgroup_get_owner(struct page *page); > > > > int page_cgroup_set_owner(struct page *page, unsigned long id); > > > > int page_cgroup_copy_owner(struct page *npage, struct page *opage); > > > > > > My immediate observation is that you're not really tracking the "owner" > > > here - you're tracking an opaque 16-bit token known only to the block > > > controller in a field which - if changed by anybody other than the block > > > controller - will lead to mayhem in the block controller. I think it > > > might be clearer - and safer - to say "blkcg" or some such instead of > > > "owner" here. > > > > > > > Basically the idea here was to be as generic as possible and make this > > feature potentially available also to other subsystems, so that cgroup > > subsystems may represent whatever they want with the 16-bit token. > > However, no more than a single subsystem may be able to use this feature > > at the same time. > > > > > I'm tempted to say it might be better to just add a pointer to your > > > throtl_grp structure into struct page_cgroup. Or maybe replace the > > > mem_cgroup pointer with a single pointer to struct css_set. Both of > > > those ideas, though, probably just add unwanted extra overhead now to gain > > > generality which may or may not be wanted in the future. > > > > The pointer to css_set sounds good, but it would add additional space to > > the page_cgroup struct. Now, page_cgroup is 40 bytes (in 64-bit arch) > > and all of them are allocated at boot time. Using unused bits in > > page_cgroup->flags is a choice with no overhead from this point of view. > > I think John suggested replacing mem_cgroup pointer with css_set so that > size of the strcuture does not increase but it leads extra level of > indirection. OK, got it sorry. So, IIUC we save css_set pointer and get a struct cgroup as following: struct cgroup *cgrp = css_set->subsys[subsys_id]->cgroup; Then, for example to get the mem_cgroup reference: struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp); It seems a lot of indirections, but I may have done something wrong or there could be a simpler way to do it. Thanks, -Andrea -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx 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>