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    SubjectRe: [PATCH 06/45] FS-Cache: Recruit a couple of page flags for cache management [ver #41]
    On Thu, 20 Nov 2008 14:42:10 +0000 David Howells <dhowells@redhat.com> wrote:

    > Recruit a couple of page flags to aid in cache management. The following extra
    > flags are defined:
    >
    > (1) PG_fscache (PG_private_2)
    >
    > The marked page is backed by a local cache and is pinning resources in the
    > cache driver.
    >
    > (2) PG_fscache_write (PG_owner_priv_2)
    >
    > The marked page is being written to the local cache. The page may not be
    > modified whilst this is in progress.
    >
    > If PG_fscache is set, then things that checked for PG_private will now also
    > check for that. This includes things like truncation and page invalidation.
    > The function page_has_private() had been added to make the checks for both
    > PG_private and PG_private_2 at the same time.
    >
    > ...
    >
    > index 74b9d90..da467b2 100644
    > --- a/include/linux/page-flags.h
    > +++ b/include/linux/page-flags.h
    > @@ -79,9 +79,11 @@ enum pageflags {
    > PG_active,
    > PG_slab,
    > PG_owner_priv_1, /* Owner use. If pagecache, fs may use*/
    > + PG_owner_priv_2, /* Owner use. fs may use in pagecache */
    > PG_arch_1,
    > PG_reserved,
    > PG_private, /* If pagecache, has fs-private data */
    > + PG_private_2, /* If pagecache, has fs aux data */
    > PG_writeback, /* Page is under writeback */

    ow, that hurt. Every time someone does this I ask "how many are left"
    but nobody seems to know how to work it out.

    How many are left?

    > - if (PagePrivate(page) &&
    > + if (page_has_private(page) &&

    I'd suggest that we make PagePrivate() go away completely, to prevent
    accidental usages from sneaking back in. If that's practical.



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