• Andrew Morton's avatar
    [PATCH] rmap 7 object-based rmap · cab971db
    Andrew Morton authored
    From: Hugh Dickins <hugh@veritas.com>
    
    Dave McCracken's object-based reverse mapping scheme for file pages: why
    build up and tear down chains of pte pointers for file pages, when
    page->mapping has i_mmap and i_mmap_shared lists of all the vmas which
    might contain that page, and it appears at one deterministic position
    within the vma (unless vma is nonlinear - see next patch)?
    
    Has some drawbacks: more work to locate the ptes from page_referenced and
    try_to_unmap, especially if the i_mmap lists contain a lot of vmas covering
    different ranges; has to down_trylock the i_shared_sem, and hope that
    doesn't fail too often.  But attractive in that it uses less lowmem, and
    shifts the rmap burden away from the hot paths, to swapout.
    
    Hybrid scheme for the moment: carry on with pte_chains for anonymous pages,
    that's unchanged; but file pages keep mapcount in the pte union of struct
    page, where anonymous pages keep chain pointer or direct pte address: so
    page_mapped(page) works on both.
    
    Hugh massaged it a little: distinct page_add_file_rmap entry point; list
    searches check rss so as not to waste time on mms fully swapped out; check
    mapcount to terminate once all ptes have been found; and a WARN_ON if
    page_referenced should have but couldn't find all the ptes.
    cab971db
mremap.c 10.2 KB