Very aggressive memory reclaim

[John Lepikhin]

Hello,

I use high-loaded machine with 10M+ inodes inside XFS, 50+ GB of
memory, intensive HDD traffic and 20..50 forks per second. Vanilla
kernel 2.6.37.4. The problem is that kernel frees memory very
aggressively.

For example:

25% of memory is used by processes
50% for page caches
7% for slabs, etc.
18% free.

That's bad but works. After few hours:

25% of memory is used by processes
62% for page caches
7% for slabs, etc.
5% free.

Most of files are cached, works perfectly. This is the moment when
kernel decides to free some memory. After memory reclaim:

25% of memory is used by processes
25% for page caches(!)
7% for slabs, etc.
43% free(!)

Page cache is dropped, server becomes too slow. This is the beginning
of new cycle.

I didn't found any huge mallocs at that moment. Looks like because of
large number of small mallocs (forks) kernel have pessimistic forecast
about future memory usage and frees too much memory. Is there any
options of tuning this? Any other variants?

Thanks!
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