lkml.org 
[lkml]   [2005]   [Aug]   [5]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [RFC] Demand faulting for large pages
    On Fri, Aug 05, 2005 at 11:37:27AM -0500, Adam Litke wrote:
    > On Fri, 2005-08-05 at 10:53, Andi Kleen wrote:
    > > On Fri, Aug 05, 2005 at 10:21:38AM -0500, Adam Litke wrote:
    > > > Below is a patch to implement demand faulting for huge pages. The main
    > > > motivation for changing from prefaulting to demand faulting is so that
    > > > huge page allocations can follow the NUMA API. Currently, huge pages
    > > > are allocated round-robin from all NUMA nodes.
    > >
    > > I think matching DEFAULT is better than having a different default for
    > > huge pages than for small pages.
    >
    > I am not exactly sure what the above means. Is 'DEFAULT' a system
    > default numa allocation policy?

    It's one of the four numa policies: DEFAULT, PREFERED, INTERLEAVE, BIND

    It just means allocate on the local node if possible, otherwise fall back.

    You said you wanted INTERLEAVE by default, which i think is a bad idea.
    It should be only optional like in all other allocations.


    > > > patch just moves the logic from hugelb_prefault() to
    > > > hugetlb_pte_fault().
    > >
    > > Are you sure you fixed get_user_pages to handle this properly? It doesn't
    > > like it.
    >
    > Unless I am missing something, the call to follow_hugetlb_page() in
    > get_user_pages() is just an optimization. Removing it means
    > follow_page() will be called individually for each PAGE_SIZE page in the
    > huge page. We can probably do better but I didn't want to cloud this
    > patch with that logic.

    The problem is that get_user_pages needs to handle the case of a large
    page not yet being faulted in properly. The SLES9 implementation did
    some changes for this.

    You don't change it at all, so I'm suspect it doesn't work yet.

    It's a common case - think people doing raw IO on huge pages shared memory.

    -Andi
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2005-08-05 18:53    [W:3.847 / U:0.008 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site