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. > > I don't know that it's right to add the burden to copy the original > value to everything that wants to use page->private. > How many such places are there? 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
