Re: [PATCH] mm/readahead.c: update the LRU positions of in-core pages, too

From: Minchan Kim
Date: Wed Jan 27 2010 - 02:09:46 EST

Hi, Wu.

I have missed this thread until now.
Before review, first of all, Thanks for adding to good feature, Chris and Wu.
I have some questions.

2010/1/21 Wu Fengguang <fengguang.wu@xxxxxxxxx>:

> Years ago I wrote a similar function, which can be called for both
> in-kernel-readahead (when it decides not to bring in new pages, but
> only retain existing pages) and fadvise-readahead (where it want to
> read new pages as well as retain existing pages).

Why doesn't it merged into mainline?
It's private patch or has some problem?

Actually I am worried about this patch.
That's because it makes shortcut promotion in reclaim exceptionally.

Of course If readahead is working well, this patch effect also would
be good. But let's think about it.

This patch effect happens when inactive file list is small, I think.
It means it's high memory pressure. so if we move ra pages into
head of inactive list, other application which require free page urgently
suffer from latency or are killed.

If VM don't have this patch, of course ra pages are discarded and
then I/O performance would be bad. but as I mentioned, it's time
high memory pressure. so I/O performance low makes system
natural throttling. It can help out of system memory pressure.

In summary I think it's good about viewpoint of I/O but I am not sure
it's good about viewpoint of system.

I will review this patch after my concern is solved. :)
Kind regards,
Minchan Kim
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