On Fri, Apr 05, 2013 at 05:31:12PM +0900, Minchan Kim wrote: >Hi Wanpeng, > >On Fri, Apr 05, 2013 at 04:22:17PM +0800, Wanpeng Li wrote: >> On Fri, Apr 05, 2013 at 05:01:06PM +0900, Minchan Kim wrote: >> >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? >> >> Hi Minchan, >> >> I can be the volunteer, what I care is if add a knob make sense? > >Frankly sepaking, I'd like to avoid new knob but there might be >some workloads suffered from mlocked page migration so we coudn't >dismiss it. In such case, introducing the knob would be a solution >with default enabling. If we don't have any report for a long time, >we can remove the knob someday, IMHO. Ok, I will start coding next week. ;-) Regards, Wanpeng Li > >Thanks. > >-- >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>