On Mon, Mar 14, 2011 at 07:41:13PM -0700, Greg Thelen wrote: > On Mon, Mar 14, 2011 at 1:23 PM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > On Mon, Mar 14, 2011 at 11:29:17AM -0700, Greg Thelen wrote: > > > > [..] > >> > We could just crawl the memcg's page LRU and bring things under control > >> > that way, couldn't we? That would fix it. What were the reasons for > >> > not doing this? > >> > >> My rational for pursuing bdi writeback was I/O locality. I have heard that > >> per-page I/O has bad locality. Per inode bdi-style writeback should have better > >> locality. > >> > >> My hunch is the best solution is a hybrid which uses a) bdi writeback with a > >> target memcg filter and b) using the memcg lru as a fallback to identify the bdi > >> that needed writeback. I think the part a) memcg filtering is likely something > >> like: > >> http://marc.info/?l=linux-kernel&m=129910424431837 > >> > >> The part b) bdi selection should not be too hard assuming that page-to-mapping > >> locking is doable. > > > > Greg, > > > > IIUC, option b) seems to be going through pages of particular memcg and > > mapping page to inode and start writeback on particular inode? > > Yes. > > > If yes, this might be reasonably good. In the case when cgroups are not > > sharing inodes then it automatically maps one inode to one cgroup and > > once cgroup is over limit, it starts writebacks of its own inode. > > > > In case inode is shared, then we get the case of one cgroup writting > > back the pages of other cgroup. Well I guess that also can be handeled > > by flusher thread where a bunch or group of pages can be compared with > > the cgroup passed in writeback structure. I guess that might hurt us > > more than benefit us. > > Agreed. For now just writing the entire inode is probably fine. > > > IIUC how option b) works then we don't even need option a) where an N level > > deep cache is maintained? > > Originally I was thinking that bdi-wide writeback with memcg filter > was a good idea. But this may be unnecessarily complex. Now I am > agreeing with you that option (a) may not be needed. Memcg could > queue per-inode writeback using the memcg lru to locate inodes > (lru->page->inode) with something like this in > [mem_cgroup_]balance_dirty_pages(): > > while (memcg_usage() >= memcg_fg_limit) { > inode = memcg_dirty_inode(cg); /* scan lru for a dirty page, then > grab mapping & inode */ > sync_inode(inode, &wbc); > } Is it possible to pass mem_cgroup in writeback_control structure or in work structure which in turn will be set in writeback_control. And modify writeback_inodes_wb() which will look that ->mem_cgroup is set. So instead of calling queue_io() it can call memcg_queue_io() and then memory cgroup can look at lru list and take its own decision on which inodes needs to be pushed for IO? Thanks Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
