On Thu, Mar 10, 2011 at 02:11:15PM -0500, Vivek Goyal wrote: > On Thu, Mar 10, 2011 at 10:57:52AM -0800, Justin TerAvest wrote: > > On Thu, Mar 10, 2011 at 10:15 AM, Vivek Goyal <vgoyal@xxxxxxxxxx> wrote: > > > On Thu, Mar 10, 2011 at 10:08:03AM -0800, Justin TerAvest wrote: > > > > > > [..] > > >> > I don't like to increase size of page_cgroup but I think you can record > > >> > information without increasing size of page_cgroup. > > >> > > > >> > A) As Andrea did, encode it to pc->flags. > > >> > But I'm afraid that there is a racy case because memory cgroup uses some > > >> > test_and_set() bits. > > >> > B) I wonder why the information cannot be recorded in page->private. > > >> > When page has buffers, you can record the information to buffer struct. > > >> > About swapio (if you take care of), you can record information to bio. > > >> > > >> Hi Kame, > > >> > > >> I'm concerned that by using something like buffer_heads stored in > > >> page->private, we will only be supported on some filesystems and not > > >> others. In addition, I'm not sure if all filesystems attach buffer > > >> heads at the same time; if page->private is modified in the flusher > > >> thread, we might not be able to determine the thread that dirtied the > > >> page in the first place. > > > > > > I think the person who dirtied the page can store the information in > > > page->private (assuming buffer heads were not generated) and if flusher > > > thread later ends up generating buffer heads and ends up modifying > > > page->private, this can be copied in buffer heads? > > > > This scares me a bit. > > > > As I understand it, fs/ code expects total ownership of page->private. > > This adds a responsibility for every user to copy the data through and > > store it in the buffer head (or anything else). btrfs seems to do > > something entirely different in some cases and store a different kind > > of value. > > If filesystems are using page->private for some other purpose also, then > I guess we have issues. > > I am ccing linux-fsdevel to have some feedback on the idea of trying > to store cgroup id of page dirtying thread in page->private and/or buffer > head for tracking which group originally dirtied the page in IO controller > during writeback. A quick "grep" showed that btrfs, ceph and logfs are using page->private for other purposes also. I was under the impression that either page->private is null or it points to buffer heads for the writeback case. So storing the info directly in either buffer head directly or first in page->private and then transferring it to buffer heads would have helped. 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
