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SubjectRe: [PATCH 5/6] writeback: sync expired inodes first in background writeback
> > Are you testing for this failure scenario?  If so, can you briefly
> > describe the testing?
> Not yet.. But one possible scheme is to record the dirty time of each
> page in a debug kernel and expose them to user space. Then we can run
> any kind of workloads, and in the mean while run a background scanner
> to collect and report the distribution of dirty page ages.
> Does it sound too heavy weight? Or we may start by reporting the dirty
> inode age first. To maintain a mapping->writeback_index_wrapped_when and
> a mapping->pages_dirtied_when to follow it (or just reuse/reset
> mapping->dirtied_when?). The former will be reset to jiffies on each
> full scan of the pages. range_whole=1 scan can maintain its start time
> in a local variable. Then we get an estimation "what's the max
> possible dirty page age this inode has?". There will sure be redirtied
> pages though..

Hmm the lighter scheme will fail the common "active sequential write
to large file" case, because the full scan will never manage to come
to an end..


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