Messages in this thread | | | Date | Mon, 12 Jul 2010 15:13:17 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH 4/6] writeback: dont redirty tail an inode with dirty pages |
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On Mon, 12 Jul 2010 23:31:27 +0800 Wu Fengguang <fengguang.wu@intel.com> wrote:
> > > + } else if (inode->i_state & I_DIRTY) { > > > + /* > > > + * At least XFS will redirty the inode during the > > > + * writeback (delalloc) and on io completion (isize). > > > + */ > > > + redirty_tail(inode); > > > > I'd drop the mention of XFS here - any filesystem that does delayed > > allocation or unwritten extent conversion after Io completion will > > cause this. Perhaps make the comment: > > > > /* > > * Filesystems can dirty the inode during writeback > > * operations, such as delayed allocation during submission > > * or metadata updates after data IO completion. > > */ > > Thanks, comments updated accordingly. > > --- > writeback: don't redirty tail an inode with dirty pages > > This avoids delaying writeback for an expired (XFS) inode with lots of > dirty pages, but no active dirtier at the moment. Previously we only do > that for the kupdate case. >
You didn't actually explain the _reason_ for making this change. Please always do that.
The patch is... surprisingly complicated, although the end result looks OK. This is not aided by the partial duplication between mapping_tagged(PAGECACHE_TAG_DIRTY) and I_DIRTY_PAGES. I don't think we can easily remove I_DIRTY_PAGES because it's used for the did-someone-just-dirty-a-page test here.
This code is way too complex and fragile and I fear that anything we do to it will break something :(
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