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    SubjectRe: [PATCH -mm 16/25] SHM_LOCKED pages are non-reclaimable
    On Fri, 6 Jun 2008 18:05:14 -0700
    Andrew Morton <akpm@linux-foundation.org> wrote:

    > > While working with Nick Piggin's mlock patches,
    >
    > Change log refers to information which its reader has not got a hope
    > of actually locating.

    Fixed that, and renamed everything to "unevictable".

    > > Use the AS_NORECLAIM flag to mark address_space of SHM_LOCKed
    > > shared memory regions as non-reclaimable. Then these pages
    > > will be culled off the normal LRU lists during vmscan.
    >
    > So I guess there's more justification for handling these pages in this
    > manner, because someone could come along later and unlock them. But
    > that isn't true of /dev/ram0 pages and ramfs pages, etc.

    Bingo. Ramdisk and ramfs pages will never become evictable again,
    while the pages in an SHM_LOCKED segment might.

    > > +static void check_move_noreclaim_page(struct page *page, struct zone *zone)
    > > +{
    > > +
    > > + ClearPageNoreclaim(page); /* for page_reclaimable() */
    >
    > Confused. Didn't we just lose track of our NR_NORECLAIM accounting?
    >
    > > + if (page_reclaimable(page, NULL)) {
    > > + enum lru_list l = LRU_INACTIVE_ANON + page_file_cache(page);
    > > + __dec_zone_state(zone, NR_NORECLAIM);

    No, we decrement the zone count here if the page is indeed
    unevictable.

    > > + list_move(&page->lru, &zone->list[l]);
    > > + __inc_zone_state(zone, NR_INACTIVE_ANON + l);
    > > + } else {
    > > + /*
    > > + * rotate noreclaim list
    > > + */
    > > + SetPageNoreclaim(page);
    > > + list_move(&page->lru, &zone->list[LRU_NORECLAIM]);
    > > + }
    > > +}

    Or mark it unevictable again if it still is.

    > > + * scan_mapping_noreclaim_pages - scan an address space for reclaimable pages
    > > + * @mapping: struct address_space to scan for reclaimable pages
    > > + *
    > > + * Scan all pages in mapping. Check non-reclaimable pages for
    > > + * reclaimability and move them to the appropriate zone lru list.
    > > + */
    > > +void scan_mapping_noreclaim_pages(struct address_space *mapping)
    > > +{

    > This function can spend fantastically large amounts of time under
    > spin_lock_irq().

    I'll leave it up to Lee and Kosaki-san to fix this, once
    you have the cleaned up versions.

    Fixing this now would just delay my other janitorial work on
    this patch series...

    --
    All Rights Reversed


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