KAMEZAWA Hiroyuki wrote: > (2012/03/20 4:59), Konstantin Khlebnikov wrote: > >> KAMEZAWA Hiroyuki wrote: >>> This is just an RFC...test is not enough yet. >>> >>> I know it's merge window..this post is just for sharing idea. >>> >>> This patch merges pc->flags and pc->mem_cgroup into a word. Then, >>> memcg's overhead will be 8bytes per page(4096bytes?). >>> >>> Because this patch will affect all memory cgroup developers, I'd like to >>> show patches before MM Summit. I think we can agree the direction to >>> reduce size of page_cgroup..and finally integrate into 'struct page' >>> (and remove cgroup_disable= boot option...) >>> >>> Patch 1/3 - introduce pc_to_mem_cgroup and hide pc->mem_cgroup >>> Patch 2/3 - remove pc->mem_cgroup >>> Patch 3/3 - remove memory barriers. >>> >>> I'm now wondering when this change should be merged.... >>> >> >> This is cool, but maybe we should skip this temporary step and merge all this stuff into page->flags. > > > Why we should skip and delay reduction of size of page_cgroup > which is considered as very big problem ? I think it would be better to solve problem completely and kill page_cgroup in one step. > >> I think we can replace zone-id and node-id in page->flags with cumulative dynamically allocated lruvec-id, >> so there will be enough space for hundred cgroups even on 32-bit systems. > > > Where section-id is ? > IIUC, now, page->section->zone/node is calculated if CONFIG_SPARSEMEM. Yeah, sections are biggest problem there. I hope we can unravel this knot. In the worst case we can extend page->flags upto 64-bits. > > BTW, I doubt that we can modify page->flags dynamically with multi-bit operations...using > cmpxchg per each page when it's charged/uncharged/other ? we can do atomic_xor(&page->flags, new-lruvec-id ^ old-lruvec-id) or atomic_add(&page->flags, new-lruvec-id - old-lruvec-id) they should work faster than cmpxchg > >> >> After lru_lock splitting page to lruvec translation will be much frequently used than page to zone, >> so page->zone and page->node translations can be implemented as page->lruvec->zone and page->lruvec->node. >> > > And need to take rcu_read_lock() around page_zone() ? Hmm, it depends. For kernel-pages there will be pointer to root-lruvec, so no protection required. If we hold lru_lock we also don't need this rcu_read_lock. > > Thanks, > -Kame > > > -- 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>