Re: fadvise DONTNEED implementation (or lack thereof)
From: Rik van Riel
Date: Wed Nov 17 2010 - 22:25:23 EST
On 11/17/2010 09:47 PM, Minchan Kim wrote:
On Thu, Nov 18, 2010 at 1:22 AM, Rik van Riel<riel@xxxxxxxxxx> wrote:
On 11/17/2010 05:16 AM, Minchan Kim wrote:
Absolutely. But how about rsync's two touch?
It can evict working set.
I need the time for investigation.
Thanks for the comment.
Maybe we could exempt MADV_SEQUENTIAL and FADV_SEQUENTIAL
touches from promoting the page to the active list?
The problem is non-mapped file page.
non-mapped file page promotion happens by only mark_page_accessed.
But it doesn't enough information to prevent promotion(ex, vma or file)
I believe we have enough information in filemap.c and can just
pass that as a parameter to mark_page_accessed.
Here is another idea.
Current problem is following as.
User can use fadivse with FADV_DONTNEED.
But problem is that it can't affect when it meet dirty pages.
So user have to sync dirty page before calling fadvise with FADV_DONTNEED.
It would lose performance.
Let's add some semantic of FADV_DONTNEED.
It invalidates only pages which are not dirty.
If it meets dirty page, let's move the page into inactive's tail or head.
If we move the page into tail, shrinker can move it into head again
for deferred write if it isn't written the backed device.
That sounds like a good idea.
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