On Mon, 13 Dec 2010 16:51:40 -0800
Michel Lespinasse <walken@xxxxxxxxxx> wrote:
> On Thu, Dec 9, 2010 at 10:11 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > On Wednesday, December 8, 2010, Michel Lespinasse <walken@xxxxxxxxxx> wrote:
> >>
> >> Yes, patch 1/6 changes the long hold time to be in read mode instead
> >> of write mode, which is only a band-aid. But, this prepares for patch
> >> 5/6, which releases mmap_sem whenever there is contention on it or
> >> when blocking on disk reads.
> >
> > I have to say that I'm not a huge fan of that horribly kludgy
> > contention check case.
> >
> > The "move page-in to read-locked sequence" and the changes to
> > get_user_pages look fine, but the contention thing is just disgusting.
> > I'd really like to see some other approach if at all possible.
>
> Andrew, should I amend my patches to remove the rwsem_is_contended() code ?
> This would involve:
> - remove rwsem-implement-rwsem_is_contended.patch and
> x86-rwsem-more-precise-rwsem_is_contended-implementation.patch
> - in mlock-do-not-hold-mmap_sem-for-extended-periods-of-time.patch,
> drop the one hunk making use of rwsem_is_contended (rest of the patch
> would still work without it)
I think I fixed all that up.
> - optionally, follow up patch to limit batch size to a constant
> in do_mlock_pages():
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index 569ae6a..a505a7e 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -457,15 +457,23 @@ static int do_mlock_pages(unsigned long start, size_t len)
> continue;
> if (nstart < vma->vm_start)
> nstart = vma->vm_start;
> + /*
> + * Constrain batch size to limit mmap_sem hold time.
> + */
> + if (nend > nstart + 1024 * PAGE_SIZE)
> + nend = nstart + 1024 * PAGE_SIZE;
> /*
> * Now fault in a range of pages. __mlock_vma_pages_range()
> * double checks the vma flags, so that it won't mlock pages
> * if the vma was already munlocked.
> */
> ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
> if (ret < 0) {
> ret = __mlock_posix_error_return(ret);
> break;
> + } else if (locked) {
> + locked = 0;
> + up_read(&mm->mmap_sem);
> }
> nend = nstart + ret * PAGE_SIZE;
> ret = 0;
>
>
> I don't really prefer using a constant, but I'm not sure how else to make
> Linus happy :)
rwsem_is_contended() didn't seem so bad to me.
Reading 1024 pages can still take a long time. I can't immediately
think of a better approach though.
--
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>