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    SubjectRe: [PATCHv4 14/39] thp, mm: rewrite delete_from_page_cache() to support huge pages
    Date
    Dave Hansen wrote:
    > On 05/11/2013 06:23 PM, Kirill A. Shutemov wrote:
    > > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
    > >
    > > As with add_to_page_cache_locked() we handle HPAGE_CACHE_NR pages a
    > > time.
    > >
    > > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
    > > ---
    > > mm/filemap.c | 31 +++++++++++++++++++++++++------
    > > 1 file changed, 25 insertions(+), 6 deletions(-)
    > >
    > > diff --git a/mm/filemap.c b/mm/filemap.c
    > > index b0c7c8c..657ce82 100644
    > > --- a/mm/filemap.c
    > > +++ b/mm/filemap.c
    > > @@ -115,6 +115,9 @@
    > > void __delete_from_page_cache(struct page *page)
    > > {
    > > struct address_space *mapping = page->mapping;
    > > + bool thp = PageTransHuge(page) &&
    > > + IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE_PAGECACHE);
    > > + int nr;
    >
    > Is that check for the config option really necessary? How would we get
    > a page with PageTransHuge() set without it being enabled?

    I'll drop it and use hpagecache_nr_page() instead.

    > I like to rewrite your code. :)

    It's nice. Thanks.

    > Which reminds me... Why do we handle their reference counts differently? :)
    >
    > It seems like we could easily put a for loop in delete_from_page_cache()
    > that will release their reference counts along with the head page.
    > Wouldn't that make the code less special-cased for tail pages?

    delete_from_page_cache() is not the only user of
    __delete_from_page_cache()...

    It seems I did it wrong in add_to_page_cache_locked(). We shouldn't take
    references on tail pages there, only one on head. On split it will be
    distributed properly.

    > > /* Leave page->index set: truncation lookup relies upon it */
    > > - mapping->nrpages--;
    > > - __dec_zone_page_state(page, NR_FILE_PAGES);
    > > + mapping->nrpages -= nr;
    > > + __mod_zone_page_state(page_zone(page), NR_FILE_PAGES, -nr);
    > > if (PageSwapBacked(page))
    > > - __dec_zone_page_state(page, NR_SHMEM);
    > > + __mod_zone_page_state(page_zone(page), NR_SHMEM, -nr);
    > > BUG_ON(page_mapped(page));
    >
    > Man, we suck:
    >
    > __dec_zone_page_state()
    > and
    > __mod_zone_page_state()
    >
    > take a differently-typed first argument. <sigh>
    >
    > Would there be any good to making __dec_zone_page_state() check to see
    > if the page we passed in _is_ a compound page, and adjusting its
    > behaviour accordingly?

    Yeah, it would be better but I think it outside the scope of the patchset.
    Probably, later.

    --
    Kirill A. Shutemov


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