On Fri, Apr 05, 2013 at 02:47:25PM +0800, Simon Jeons wrote: > Hi Minchan, > On 04/03/2013 09:11 AM, Minchan Kim wrote: > >On Tue, Apr 02, 2013 at 03:15:23PM -0700, Hugh Dickins wrote: > >>On Tue, 2 Apr 2013, Kirill A. Shutemov wrote: > >>>Kirill A. Shutemov wrote: > >>>>From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> > >>>> > >>>>ramfs is the most simple fs from page cache point of view. Let's start > >>>>transparent huge page cache enabling here. > >>>> > >>>>For now we allocate only non-movable huge page. It's not yet clear if > >>>>movable page is safe here and what need to be done to make it safe. > >>>> > >>>>Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > >>>>--- > >>>> fs/ramfs/inode.c | 6 +++++- > >>>> 1 file changed, 5 insertions(+), 1 deletion(-) > >>>> > >>>>diff --git a/fs/ramfs/inode.c b/fs/ramfs/inode.c > >>>>index c24f1e1..da30b4f 100644 > >>>>--- a/fs/ramfs/inode.c > >>>>+++ b/fs/ramfs/inode.c > >>>>@@ -61,7 +61,11 @@ struct inode *ramfs_get_inode(struct super_block *sb, > >>>> inode_init_owner(inode, dir, mode); > >>>> inode->i_mapping->a_ops = &ramfs_aops; > >>>> inode->i_mapping->backing_dev_info = &ramfs_backing_dev_info; > >>>>- mapping_set_gfp_mask(inode->i_mapping, GFP_HIGHUSER); > >>>>+ /* > >>>>+ * TODO: what should be done to make movable safe? > >>>>+ */ > >>>>+ mapping_set_gfp_mask(inode->i_mapping, > >>>>+ GFP_TRANSHUGE & ~__GFP_MOVABLE); > >>>Hugh, I've found old thread with the reason why we have GFP_HIGHUSER here, not > >>>GFP_HIGHUSER_MOVABLE: > >>> > >>>http://lkml.org/lkml/2006/11/27/156 > >>> > >>>It seems the origin reason is not longer valid, correct? > >>Incorrect, I believe: so far as I know, the original reason remains > >>valid - though it would only require a couple of good small changes > >>to reverse that - or perhaps you have already made these changes? > >> > >>The original reason is that ramfs pages are not migratable, > >>therefore they should be allocated from an unmovable area. > >> > >>As I understand it (and I would have preferred to run a test to check > >>my understanding before replying, but don't have time for that), ramfs > >>pages cannot be migrated for two reasons, neither of them a good reason. > >> > >>One reason (okay, it wouldn't have been quite this way in 2006) is that > >>ramfs (rightly) calls mapping_set_unevictable(), so its pages will fail > >>the page_evictable() test, so they will be marked PageUnevictable, so > >>__isolate_lru_page() will refuse to isolate them for migration (except > >>for CMA). > >True. > > > >>I am strongly in favour of removing that limitation from > >>__isolate_lru_page() (and the thread you pointed - thank you - shows Mel > >>and Christoph were both in favour too); and note that there is no such > >>restriction in the confusingly similar but different isolate_lru_page(). > >> > >>Some people do worry that migrating Mlocked pages would introduce the > >>occasional possibility of a minor fault (with migration_entry_wait()) > >>on an Mlocked region which never faulted before. I tend to dismiss > >>that worry, but maybe I'm wrong to do so: maybe there should be a > >>tunable for realtimey people to set, to prohibit page migration from > >>mlocked areas; but the default should be to allow it. > >I agree. > >Just FYI for mlocked page migration > > > >I tried migratioin of mlocked page and Johannes and Mel had a concern > >about that. > >http://lkml.indiana.edu/hypermail/linux/kernel/1109.0/00175.html > > > >But later, Peter already acked it and I guess by reading the thread that > >Hugh was in favour when page migration was merged first time. > > > >http://marc.info/?l=linux-mm&m=133697873414205&w=2 > >http://marc.info/?l=linux-mm&m=133700341823358&w=2 > > > >Many people said mlock means memory-resident, NOT pinning so it could > >allow minor fault while Mel still had a concern except CMA. > >http://marc.info/?l=linux-mm&m=133674219714419&w=2 > > How about add a knob? Maybe, volunteering? -- Kind regards, Minchan Kim -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>