Messages in this thread Patch in this message | | | Subject | Re: [PATCH] UBIFS: Implement ->migratepage() | From | Vlastimil Babka <> | Date | Thu, 17 Mar 2016 10:57:41 +0100 |
| |
+CC Hugh, Mel
On 03/16/2016 11:55 PM, Richard Weinberger wrote: > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> > > When using CMA during page migrations UBIFS might get confused
It shouldn't be CMA specific, the same code runs from compaction, autonuma balancing...
> and the following assert triggers: > UBIFS assert failed in ubifs_set_page_dirty at 1451 (pid 436) > > UBIFS is using PagePrivate() which can have different meanings across > filesystems. Therefore the generic page migration code cannot handle this > case correctly. > We have to implement our own migration function which basically does a > plain copy but also duplicates the page private flag.
Lack of PagePrivate() migration is surely a bug, but at a glance of how UBIFS uses the flag, it's more about accounting, it shouldn't prevent a page from being marked PageDirty()? I suspect your initial bug (which is IIUC the fact that there's a dirty pte, but PageDirty(page) is false) comes from the generic fallback_migrate_page() which does:
if (PageDirty(page)) { /* Only writeback pages in full synchronous migration */ if (mode != MIGRATE_SYNC) return -EBUSY; return writeout(mapping, page); }
And writeout() seems to Clear PageDirty() through clear_page_dirty_for_io() but I'm not so sure about the pte (or pte's in all rmaps). But this comment in the latter function:
* Yes, Virginia, this is indeed insane.
scared me enough to not investigate further. Hopefully the people I CC'd understand more about page migration than me. I'm just an user :)
In any case, this patch would solve both lack of PageDirty() transfer, and avoid the path leading from fallback_migrate_page() to writeout(). But I'm not confident enough here to ack it.
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > [rw: Massaged changelog] > Signed-off-by: Richard Weinberger <richard@nod.at> > --- > fs/ubifs/file.c | 20 ++++++++++++++++++++ > 1 file changed, 20 insertions(+) > > diff --git a/fs/ubifs/file.c b/fs/ubifs/file.c > index 0edc128..48b2944 100644 > --- a/fs/ubifs/file.c > +++ b/fs/ubifs/file.c > @@ -52,6 +52,7 @@ > #include "ubifs.h" > #include <linux/mount.h> > #include <linux/slab.h> > +#include <linux/migrate.h> > > static int read_block(struct inode *inode, void *addr, unsigned int block, > struct ubifs_data_node *dn) > @@ -1452,6 +1453,24 @@ static int ubifs_set_page_dirty(struct page *page) > return ret; > } > > +static int ubifs_migrate_page(struct address_space *mapping, > + struct page *newpage, struct page *page, enum migrate_mode mode) > +{ > + int rc; > + > + rc = migrate_page_move_mapping(mapping, newpage, page, NULL, mode, 0); > + if (rc != MIGRATEPAGE_SUCCESS) > + return rc; > + > + if (PagePrivate(page)) { > + ClearPagePrivate(page); > + SetPagePrivate(newpage); > + } > + > + migrate_page_copy(newpage, page); > + return MIGRATEPAGE_SUCCESS; > +} > + > static int ubifs_releasepage(struct page *page, gfp_t unused_gfp_flags) > { > /* > @@ -1591,6 +1610,7 @@ const struct address_space_operations ubifs_file_address_operations = { > .write_end = ubifs_write_end, > .invalidatepage = ubifs_invalidatepage, > .set_page_dirty = ubifs_set_page_dirty, > + .migratepage = ubifs_migrate_page, > .releasepage = ubifs_releasepage, > }; > >
| |