On 03/03/2015 07:45 PM, Eric B Munson wrote: > On Tue, 03 Mar 2015, Vlastimil Babka wrote: > >> On 03/03/2015 06:41 PM, Eric B Munson wrote:> All, >> > >> > After LSF/MM last year Peter revived a patch set that would create >> > infrastructure for pinning pages as opposed to simply locking them. >> > AFAICT, there was no objection to the set, it just needed some help >> > from the IB folks. >> > >> > Am I missing something about why it was never merged? I ask because >> > Akamai has bumped into the disconnect between the mlock manpage, >> > Documentation/vm/unevictable-lru.txt, and reality WRT compaction and >> > locking. A group working in userspace read those sources and wrote a >> > tool that mmaps many files read only and locked, munmapping them when >> > they are no longer needed. Locking is used because they cannot afford a >> > major fault, but they are fine with minor faults. This tends to >> > fragment memory badly so when they started looking into using hugetlbfs >> > (or anything requiring order > 0 allocations) they found they were not >> > able to allocate the memory. They were confused based on the referenced >> > documentation as to why compaction would continually fail to yield >> > appropriately sized contiguous areas when there was more than enough >> > free memory. >> >> So you are saying that mlocking (VM_LOCKED) prevents migration and thus >> compaction to do its job? If that's true, I think it's a bug as it is AFAIK >> supposed to work just fine. > > Agreed. But as has been discussed in the threads around the VM_PINNED > work, there are people that are relying on the fact that VM_LOCKED > promises no minor faults. Which is why the behavoir has remained. At least in the VM_PINNED thread after last lsf/mm, I don't see this mentioned. I found no references to mlocking in compaction.c, and in migrate.c there's just mlock_migrate_page() with comment: /* * mlock_migrate_page - called only from migrate_page_copy() to * migrate the Mlocked page flag; update statistics. */ It also passes TTU_IGNORE_MLOCK to try_to_unmap(). So what am I missing? Where is this restriction? -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>