Hello, On Mon 06-02-12 00:14:58, Michel Lespinasse wrote: > I would like to attend the LSF/MM summit in April this year. I do not > have any formal topic proposals at this point; however there are > several MM areas I am interested in: > > - mmap_sem locking: I have done some work in the past to reduce > mmap_sem hold times when page faults wait for transfering file pages > from disk, as well as during large mlock operations. However mmap_sem > can still be held for long times today when write page faults trigger > dirty write throttling, or when the system is under memory pressure > and page allocations within the page fault handler hit the ttfp path > (I have some pending work in these areas that I'd like to submit > shortly). This is an area that hasn't been much invested in, probably > because the fact that most users only need a read lock suffices to > mask the issues in many cases. However I expect it to become more > important as we keep improving performance isolation between > processes. One way we frequently hit mmap_sem related issues at Google > is when building monitoring mechanisms that are expected to stay > responsive when the monitored systems get into bad memory pressure > situations. I'd be interested in this. Holding mmap_sem during write page faults (->page_mkwrite) is causing problems with lock ordering when handling filesystem freezing. I hope I can solve the problems by dropping mmap_sem when we see filesystem is frozen, wait for it to thaw, retake mmap_sem and return VM_FAULT_RETRY but I'd be happy for a less hacky solution... Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>