On Thu, 19 Mar 2015, Eric B Munson wrote: > Currently, pages which are marked as unevictable are protected from > compaction, but not from other types of migration. The POSIX real time > extension explicitly states that mlock() will prevent a major page > fault, but the spirit of is is that mlock() should give a process the > ability to control sources of latency, including minor page faults. > However, the mlock manpage only explicitly says that a locked page will > not be written to swap and this can cause some confusion. The > compaction code today, does not give a developer who wants to avoid swap > but wants to have large contiguous areas available any method to achieve > this state. This patch introduces a sysctl for controlling compaction > behavoir with respect to the unevictable lru. Users that demand no page > faults after a page is present can set compact_unevictable to 0 and > users who need the large contiguous areas can enable compaction on > locked memory by leaving the default value of 1. > > To illustrate this problem I wrote a quick test program that mmaps a > large number of 1MB files filled with random data. These maps are > created locked and read only. Then every other mmap is unmapped and I > attempt to allocate huge pages to the static huge page pool. When the > compact_unevictable sysctl is 0, I cannot allocate hugepages after > fragmenting memory. When the value is set to 1, allocations succeed. > > Signed-off-by: Eric B Munson <[email protected]> > Cc: Vlastimil Babka <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Christoph Lameter <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: Mel Gorman <[email protected]> > Cc: David Rientjes <[email protected]> > Cc: Rik van Riel <[email protected]> > Cc: Michal Hocko <[email protected]> > Cc: [email protected] > Cc: [email protected] > Cc: [email protected] > Cc: [email protected]
Acked-by: David Rientjes <[email protected]> -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
