On Sun, Feb 18, 2018 at 04:47:55PM +0000, [email protected] wrote: > From: "Robert M. Harris" <[email protected]> > > __fragmentation_index() calculates a value used to determine whether > compaction should be favoured over page reclaim in the event of allocation > failure. The calculation itself is opaque and, on inspection, does not > match its existing description. The function purports to return a value > between 0 and 1000, representing units of 1/1000. Barring the case of a > pathological shortfall of memory, the lower bound is instead 500. This is > significant because it is the default value of sysctl_extfrag_threshold, > i.e. the value below which compaction should be avoided in favour of page > reclaim for costly pages. > > This patch implements and documents a modified version of the original > expression that returns a value in the range 0 <= index < 1000. It amends > the default value of sysctl_extfrag_threshold to preserve the existing > behaviour. > > Signed-off-by: Robert M. Harris <[email protected]>
You have to update sysctl_extfrag_threshold as well for the new bounds. It effectively makes it a no-op but it was a no-op already and adjusting that default should be supported by data indicating it's safe. -- Mel Gorman SUSE Labs
