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    SubjectRe: [RFC][PATCH] big continuous memory allocator v2
    On Tue, 7 Sep 2010 01:37:27 -0700
    Minchan Kim <> wrote:

    > Nice cleanup.
    > There are some comments in below.
    > On Mon, Sep 6, 2010 at 7:45 PM, KAMEZAWA Hiroyuki
    > <> wrote:
    > >
    > > This is a page allcoator based on memory migration/hotplug code.
    > > passed some small tests, and maybe easier to read than previous one.
    > >
    > > ==
    > > From: KAMEZAWA Hiroyuki <>
    > >
    > > This patch as a memory allocator for contiguous memory larger than MAX_ORDER.
    > >
    > >  alloc_contig_pages(hint, size, node);
    > I have thought this patch is to be good for dumb device drivers which
    > want big contiguous
    > memory. So if some device driver want big memory and they can tolerate
    > latency or fail,
    > this is good solution, I think.
    > And some device driver can't tolerate fail, they have to use MOVABLE zone.
    > For it, I hope we have a option like ALLOC_FIXED(like MAP_FIXED).
    > That's because embedded people wanted to aware BANK of memory.
    > So if they get free page which they don't want, it can be pointless.

    > In addition, I hope it can support CROSS_ZONE migration mode.
    > Most of small system can't support swap system. So if we can't migrate
    > anon pages into other zones, external fragment problem still happens.
    Now, this code migrates pages to somewhere, including crossing zone, node etc..
    (because it just use GFP_HIGHUSER_MOVABLE)

    > I think reclaim(ex, discard file-backed pages) can become one option to prevent
    > the problem. But it's more cost so we can support it by calling mode.
    > (But it could be trivial since caller should know this function is very cost)

    > ex) alloc_contig_pages(hint, size, node, ALLOC_FIXED|ALLOC_RECLAIM);

    This migration's page allocation code will cause memory reclaim and
    kswapd wakeup if memory is in short. But hmm, there are no codes as

    reclaim_memory_within(start, end).

    But I guess if there are LRU pages within the range which cannot be migrated,
    they can't be dropped. In another consideration,

    shrink_slab_within(start, end)
    will be able to make success-rate better. (and this is good for memory hotplug, too)

    I'll start from adding ALLOC_FIXED.


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