Move cleaned pages into read cache instead of discarding them. #809
+40
−9
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Just after dirty pages have been written out to disk, they are currently discard and need to be read in again when these pages are accessed in the future.
This changes moves them into the read cache instead thereby keeping the clean data available and cache hot in memory.
It turned out that this was also what was making direct I/O slower in #808, i.e. this was not that noticeable when buffered I/O is use because the pages were read back in from the kernel page cache most of the time but it should be a win in both scenarios.