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    SubjectRe: [PATCH v4] mm: add replace_page_cache_page() function
    On Tue, 18 Jan 2011 15:28:44 -0800
    Andrew Morton <akpm@linux-foundation.org> wrote:

    > On Tue, 18 Jan 2011 12:18:11 +0100
    > Miklos Szeredi <miklos@szeredi.hu> wrote:
    >
    > > +int replace_page_cache_page(struct page *old, struct page *new, gfp_t gfp_mask)
    > > +{
    > > + int error;
    > > + struct mem_cgroup *memcg = NULL;
    >
    > I'm suspecting that the unneeded initialisation was added to suppress a
    > warning?
    >
    No.
    It's necessary for mem_cgroup_{prepare|end}_migration().
    mem_cgroup_prepare_migration() will return without doing anything in
    "if (mem_cgroup_disabled()" case(iow, "memcg" is not overwritten),
    but mem_cgroup_end_migration() depends on the value of "memcg" to decide
    whether prepare_migration has succeeded or not.
    This may not be a good implementation, but IMHO I'd like to to initialize
    valuable before using it in general.

    Thanks,
    Daisuke Nishimura.


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