Messages in this thread | | | Subject | Re: [PATCH] UBIFS: Implement ->migratepage() | From | Richard Weinberger <> | Date | Fri, 25 Mar 2016 23:53:46 +0100 |
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Am 17.03.2016 um 10:57 schrieb Vlastimil Babka: > +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.
Hugh? Mel? Anyone? :-)
It is still not clear to me whether this needs fixing in MM or UBIFS.
Thanks, //richard
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