pre4 oom too soon

From: Hugh Dickins (hugh@veritas.com)
Date: Fri Oct 05 2001 - 14:26:06 EST


2.4.11-pre4 gives me oom_kill I never got before.
All numbers decimal in 4kB pages:

num_physpages 65520
free or freeable 56000 (from MemFree after swapoff afterwards)
total_swap_pages 132526
prog tries to hog 153600

At oom_kill time:

all_zones_low yes (DMA & Normal well above min, no Highmem)
nr_swap_pages 0
page_cache_size 59013
swapper_space.nrpages 58202

I'm not sure exactly what to blame in out_of_memory(), but it does
look wrong to depend so much on whether nr_swap_pages happens to be
0 at that instant or not, and a lot of that full swap is duplicated
in the swap cache. Probably that should be taken into consideration?

(I wonder whether, before my 2.4.10 fix to lowest_bit and highest_bit
in scan_swap_map, it was rarer to find nr_swap_pages 0 - swap pages
could be free, but invisible to scan_swap_map.)

Hugh

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