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    SubjectRe: [patch] mm: disable user interface to manually rescue unevictable pages
    On Wed, Sep 28, 2011 at 11:14:24AM +0900, Minchan Kim wrote:
    > On Tue, Sep 27, 2011 at 09:27:14AM +0200, Johannes Weiner wrote:
    > > At one point, anonymous pages were supposed to go on the unevictable
    > > list when no swap space was configured, and the idea was to manually
    > > rescue those pages after adding swap and making them evictable again.
    > > But nowadays, swap-backed pages on the anon LRU list are not scanned
    > > without available swap space anyway, so there is no point in moving
    > > them to a separate list anymore.
    > >
    > > The manual rescue could also be used in case pages were stranded on
    > > the unevictable list due to race conditions. But the code has been
    > > around for a while now and newly discovered bugs should be properly
    > > reported and dealt with instead of relying on such a manual fixup.
    > >
    > > In addition to the lack of a usecase, the sysfs interface to rescue
    > > pages from a specific NUMA node has been broken since its
    > > introduction, so it's unlikely that anybody ever relied on that.
    > >
    > > This patch removes the functionality behind the sysctl and the
    > > node-interface and emits a one-time warning when somebody tries to
    > > access either of them.
    > >
    > > Signed-off-by: Johannes Weiner <jweiner@redhat.com>
    > > Reported-by: Kautuk Consul <consul.kautuk@gmail.com>
    > Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

    Thanks, Minchan.

    > > @@ -3469,11 +3415,8 @@ int scan_unevictable_handler(struct ctl_table *table, int write,
    > > void __user *buffer,
    > > size_t *length, loff_t *ppos)
    > > {
    > > + warn_scan_unevictable_pages();
    > > proc_doulongvec_minmax(table, write, buffer, length, ppos);
    > > -
    > > - if (write && *(unsigned long *)table->data)
    > > - scan_all_zones_unevictable_pages();
    > > -
    > > scan_unevictable_pages = 0;
    >
    > Nitpick:
    > Could we remove this resetting with zero?

    table->data = &scan_unevictable_pages, so I let it in such that the
    generic sysctl stuff to process the input and clean up afterward is
    complete.


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