On Thu, Aug 04, 2022 at 01:22:41PM +1000, Alistair Popple wrote: > When pinning pages with FOLL_LONGTERM check_and_migrate_movable_pages() > is called to migrate pages out of zones which should not contain any > longterm pinned pages. > > When migration succeeds all pages will have been unpinned so pinning > needs to be retried. Migration can also fail, in which case the pages > will also have been unpinned but the operation should not be retried. If > all pages are in the correct zone nothing will be unpinned and no retry > is required. > > The logic in check_and_migrate_movable_pages() tracks unnecessary state > and the return codes for each case are difficult to follow. Refactor the > code to clean this up. No behaviour change is intended. > > Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx> > Cc: "Sierra Guiza, Alejandro (Alex)" <alex.sierra@xxxxxxx> > Cc: Chaitanya Kulkarni <kch@xxxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: Felix Kuehling <Felix.Kuehling@xxxxxxx> > Cc: Jason Gunthorpe <jgg@xxxxxxxxxx> > Cc: John Hubbard <jhubbard@xxxxxxxxxx> > Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx> > Cc: Miaohe Lin <linmiaohe@xxxxxxxxxx> > Cc: Muchun Song <songmuchun@xxxxxxxxxxxxx> > Cc: Pasha Tatashin <pasha.tatashin@xxxxxxxxxx> > Cc: Ralph Campbell <rcampbell@xxxxxxxxxx> > > --- > > Originally posted as "mm/gup.c: Simplify and fix > check_and_migrate_movable_pages() return codes"[1]. > > Changes from that version: > > - Restore the original isolation failure behaviour and don't fail the > pup. Instead retry indefinitely. > - Unpin all pages on retry or failure rather than just failure. > > Jason - I dropped your Reviewed-by. I had to remove the changes to make > error handling follow convention as we need to always unpin the pages. > We also need the list_empty() checks because we may or may not have > pages in the list if we found coherent pages. So there isn't much I > could see to simplify, but let me know if you spot some. I don't quite understand this, if the point is to loop on the LRU indefinately, why not just code that? Why do we need to go around the big loop? Jason
