On Thu, 13 Oct 2011 18:25:06 -0700 Michel Lespinasse <walken@xxxxxxxxxx> wrote: > On Wed, Sep 28, 2011 at 1:59 AM, KAMEZAWA Hiroyuki > <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote: > > On Wed, 28 Sep 2011 01:19:50 -0700 > > Michel Lespinasse <walken@xxxxxxxxxx> wrote: > >> It tends to perform worse if we try making it multithreaded. What > >> happens is that the scanning threads call page_referenced() a lot, and > >> if they both try scanning pages that belong to the same file that > >> causes the mapping's i_mmap_mutex lock to bounce. Same things happens > >> if they try scanning pages that belong to the same anon VMA too. > >> > > > > Hmm. with brief thinking, if you can scan list of page tables, > > you can set young flags without any locks. > > For inode pages, you can hook page lookup, I think. > > It would be possible to avoid taking rmap locks by instead scanning > all page tables, and transferring the pte young bits observed there to > the PageYoung page flag. This is a significant design change, but > would indeed work. > > Just to clarify the idea, how would you go about finding all page > tables to scan ? The most straightforward approach would be iterate > over all processes and scan their address spaces, but I don't think we > can afford to hold tasklist_lock (even for reads) for so long, so we'd > have to be a bit smarter than that... I can think of a few different > ways but I'd like to know if you have something specific in mind > first. Maybe there are several idea. 1. how about chasing "pgd" kmem_cache ? I'm not sure but in x86 it seems all pgds are lined to pgd_list. Now, it's not RCU list but making it as RCU list isn't hard. Note: IIUC, struct page for pgd contains pointer to mm_struct. 2. track dup_mm and do_exec. insert hook and maintain list of mm_struct.(It's not needed to be implemented as list) 3. Like pgd_list, add some flag to pgd pages. Then, you can scan memmap and find 'pgd' page and walk into the page table tree. Hmm ? Thanks, -Kame -- 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>