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    swap: cull unevictable pages in fault path · 64d6519d
    Lee Schermerhorn 提交于
    In the fault paths that install new anonymous pages, check whether the
    page is evictable or not using lru_cache_add_active_or_unevictable().  If
    the page is evictable, just add it to the active lru list [via the pagevec
    cache], else add it to the unevictable list.
    
    This "proactive" culling in the fault path mimics the handling of mlocked
    pages in Nick Piggin's series to keep mlocked pages off the lru lists.
    
    Notes:
    
    1) This patch is optional--e.g., if one is concerned about the
       additional test in the fault path.  We can defer the moving of
       nonreclaimable pages until when vmscan [shrink_*_list()]
       encounters them.  Vmscan will only need to handle such pages
       once, but if there are a lot of them it could impact system
       performance.
    
    2) The 'vma' argument to page_evictable() is require to notice that
       we're faulting a page into an mlock()ed vma w/o having to scan the
       page's rmap in the fault path.   Culling mlock()ed anon pages is
       currently the only reason for this patch.
    
    3) We can't cull swap pages in read_swap_cache_async() because the
       vma argument doesn't necessarily correspond to the swap cache
       offset passed in by swapin_readahead().  This could [did!] result
       in mlocking pages in non-VM_LOCKED vmas if [when] we tried to
       cull in this path.
    
    4) Move set_pte_at() to after where we add page to lru to keep it
       hidden from other tasks that might walk the page table.
       We already do it in this order in do_anonymous() page.  And,
       these are COW'd anon pages.  Is this safe?
    
    [riel@redhat.com: undo an overzealous code cleanup]
    Signed-off-by: NLee Schermerhorn <lee.schermerhorn@hp.com>
    Signed-off-by: NRik van Riel <riel@redhat.com>
    Signed-off-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    64d6519d
swap.h 11.0 KB