On Tue, Feb 01, 2011 at 04:42:40PM -0800, Andrew Morton wrote: > On Tue, 1 Feb 2011 13:21:46 +0200 > Gleb Natapov <gleb@xxxxxxxxxx> wrote: > > > GUP user may want to try to acquire a reference to a page if it is already > > in memory, but not if IO, to bring it in, is needed. For example KVM may > > tell vcpu to schedule another guest process if current one is trying to > > access swapped out page. Meanwhile, the page will be swapped in and the > > guest process, that depends on it, will be able to run again. > > > > This patch adds FAULT_FLAG_RETRY_NOWAIT (suggested by Linus) and > > FOLL_NOWAIT follow_page flags. FAULT_FLAG_RETRY_NOWAIT, when used in > > conjunction with VM_FAULT_ALLOW_RETRY, indicates to handle_mm_fault that > > it shouldn't drop mmap_sem and wait on a page, but return VM_FAULT_RETRY > > instead. > > > > ... > > > > +#define FOLL_NOWAIT 0x20 /* return if disk transfer is needed */ > > The comment is a little misleading. Or incomplete. > > For both swap-backed and file-backed pages, the code will initiate the > disk transfer and will then return without waiting for it to complete. > This (important!) information isn't really presented in either the > changelog or the code itself. > > This? > Yes, this is better. Thanks you. I see that the patch below is in your queue already. Should I re-spin my patch with improved comment anyway? > --- a/include/linux/mm.h~mm-allow-gup-to-fail-instead-of-waiting-on-a-page-fix > +++ a/include/linux/mm.h > @@ -1537,7 +1537,8 @@ struct page *follow_page(struct vm_area_ > #define FOLL_GET 0x04 /* do get_page on page */ > #define FOLL_DUMP 0x08 /* give error on hole if it would be zero */ > #define FOLL_FORCE 0x10 /* get_user_pages read/write w/o permission */ > -#define FOLL_NOWAIT 0x20 /* return if disk transfer is needed */ > +#define FOLL_NOWAIT 0x20 /* if a disk transfer is needed, start the IO > + * and return without waiting upon it */ > #define FOLL_MLOCK 0x40 /* mark page as mlocked */ > #define FOLL_SPLIT 0x80 /* don't return transhuge pages, split them */ > > _ -- Gleb. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom policy in Canada: sign http://dissolvethecrtc.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>