Messages in this thread | | | Date | Fri, 18 Jan 2008 17:32:03 +0800 | From | Fengguang Wu <> | Subject | Re: [patch] Converting writeback linked lists to a tree based data structure |
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On Thu, Jan 17, 2008 at 10:43:15PM -0800, Michael Rubin wrote: > On Jan 17, 2008 8:56 PM, Fengguang Wu <wfg@mail.ustc.edu.cn> wrote: > > On Thu, Jan 17, 2008 at 01:07:05PM -0800, Michael Rubin wrote: > > Suppose we want to grant longer expiration window for temp files, > > adding a new list named s_dirty_tmpfile would be a handy solution. > > When you mean tmp do you mean files that eventually get written to
Yes, they are disk based and can be synced on.
> disk? If not I would just use the WRITEBACK_NEVER. If so I am not sure > if that feature is worth making a special case. It seems like the > location based ideas may be more useful.
I'm not interested in WRITEBACK_NEVER or location based writeback for now :-)
> > > > - refill s_io iif it is drained > > > > this prevents promotion of big/old files > > > > > > Once a big file gets its first do_writepages it is moved behind the > > > other smaller files via i_flushed_when. And the same in reverse for > > > big vs old. > > > > You mean i_flush_gen? > > Yeah sorry. It was once called i_flush_when. (sheepish) > > > No, sync_sb_inodes() will abort on every > > MAX_WRITEBACK_PAGES, and s_flush_gen will be updated accordingly. > > Hence the sync will restart from big/old files. > > If I understand you correctly I am not sure I agree. Here is what I > think happens in the patch: > > 1) pull big inode off of flush tree > 2) sync big inode > 3) Hit MAX_WRITEBACK_PAGES > 4) Re-insert big inode (without modifying the dirtied_when) > 5) update the i_flush_gen on big inode and re-insert behind small > inodes we have not synced yet. > > In a subsequent sync_sb_inode we end up retrieving the small inode we > had not serviced yet.
Yes, exactly. And then it will continue to sync the big one again. It will never be able to move forward to the next dirtied_when before exhausting the inodes in the current list(with the oldest dirtied_when).
> > > > - return from sync_sb_inodes() after one go of s_io > > > > > > I am not sure how this limit helps things out. Is this for superblock > > > starvation? Can you elaborate? > > > > We should have a way to go to next superblock even if new dirty inodes > > or pages are emerging fast in this superblock. Fill and drain s_io > > only once and then abort helps. > > Got it. > > > s_io is a stable and bounded working set in one go of superblock. > > Is this necessary with MAX_WRITEBACK_PAGES? It feels like a double limit.
We need a limit and continuing scheme at each level. It was so hard to sort them out, that I'm really reluctant to restart all the fuss again.
> > Basically you make one list_head in each rbtree node. > > That list_head is recycled cyclic, and is an analog to the old > > fashioned s_dirty. We need to know 'where we are' and 'where it ends'. > > So an extra indicator must be introduced - i_flush_gen. It's awkward. > > We are simply repeating the aged list_heads' problem. > > To me they both feel a little awkward. I feel like the original > problem in 2.6.23 led to a lot of examination which is bringing new > possibilities to light. > > BTW the issue that started me on this whole path (starving large > files) was still present in 2.6.23-rc8 but now looks fixed in > 2.6.24-rc3. > Still no idea about your changes in 2.6.24-rc6-mm1. I have given up > trying to get that thing to boot.
Hehe, I guess the bug is still there in 2.6.24-rc3. But should be gone in the latest patchset.
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