[PATCH/RFC 0/4] VM: Manual and Automatic page cache reclaim

Martin Hicks
2005-04-27T15:08:48Z

Hi,

The following set of patches is response to the first round of comments
that were sent out in February

http://marc.theaimsgroup.com/?l=linux-kernel&m=110839604924587&w=2

The consensus of this thread was that manual reclaim should happen
through a syscall and be per-node, and that automatic reclaim should
probably happen through mempolicy hints.

This set is against 2.6.12-rc2-mm2 (sorry for not being against -mm3.
It doesn't boot correctly on Altix)

The patches introduce two different ways to free up page cache from a
node: manually through a syscall and automatically through flag
modifiers to a mempolicy.

Currently if a job is started and there is page cache lying around on a
particular node then allocations will spill onto remote nodes and page
cache won't be reclaimed until the whole system is short on memory.
This can result in a signficiant performance hit for HPC applications
that planned on that memory being allocated locally.

Here's a little summary of the pages in the set:

1/4: Merge LRU pages

This is the opposite of isolate_lru_pages(). It merges pages from
a list back onto the appropriate LRU lists.

2/4: Local reclaim core

The reclaim code. It extends shrink_list() so it can be used to scan
the active list as well. The core of all of this is
reclaim_clean_pages(). It tries to remove a specified number of pages
from a zone's cache. It does this without swapping or doing writebacks.
The goal here is to free easily freeable pages.

3/4: toss_page_cache_node() syscall

This adds the manual reclaim method via a syscall.

4/4: localreclaim flags for mempolicies

Adds a flags argument to set_mempolicy() and add a new mempolicy.

mh

--
Martin Hicks || Silicon Graphics Inc. || mort@sgi.com