On Mon, 26 Sep 2011 13:29:45 +0200
Johannes Weiner [off-list ref] wrote:

On Sun, Sep 25, 2011 at 04:29:40PM +0530, Kautuk Consul wrote:

quoted

write_scan_unavictable_node checks the value req returned by
strict_strtoul and returns 1 if req is 0.

However, when strict_strtoul returns 0, it means successful conversion
of buf to unsigned long.

Due to this, the function was not proceeding to scan the zones for
unevictable pages even though we write a valid value to the 
scan_unevictable_pages sys file.

Given that there is not a real reason for this knob (anymore) and that
it apparently never really worked since the day it was introduced, how
about we just drop all that code instead?

Yes, let's remove it if at all possible.

However, to be nice to people I do think we should emit a once-per-boot
printk when someone tries to use it, then remove it for real at least a
couple of kernel cycles later.  Just in case someone's script or tuning
app is trying to open that procfs file.

---
From: Johannes Weiner <redacted>
Subject: mm: remove sysctl to manually rescue unevictable pages

At one point, anonymous pages were supposed to go on the unevictable
list when no swap space was configured, and the idea was to manually
rescue those pages after adding swap and making them evictable again.
But nowadays, swap-backed pages on the anon LRU list are not scanned
without available swap space anyway, so there is no point in moving
them to a separate list anymore.

The manual rescue could also be used in case pages were stranded on
the unevictable list due to race conditions.  But the code has been
around for a while now and newly discovered bugs should be properly
reported and dealt with instead of relying on such a manual fixup.

Signed-off-by: Johannes Weiner <redacted>

The changelog failed to note that the sysctl doesn't actually *work*. 
This is a pretty strong argument for removing it ;)

Also, a reported-by:Kautuk would have been nice.

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