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    SubjectRe: [PATCH mmotm] mm: alloc_large_system_hash check order
    Hugh Dickins a écrit :
    > On Thu, 30 Apr 2009, Mel Gorman wrote:
    >> On Wed, Apr 29, 2009 at 10:09:48PM +0100, Hugh Dickins wrote:
    >>> On an x86_64 with 4GB ram, tcp_init()'s call to alloc_large_system_hash(),
    >>> to allocate tcp_hashinfo.ehash, is now triggering an mmotm WARN_ON_ONCE on
    >>> order >= MAX_ORDER - it's hoping for order 11. alloc_large_system_hash()
    >>> had better make its own check on the order.

    Well, I dont know why, since alloc_large_system_hash() already take
    care of retries, halving size between each tries.

    >>>
    >>> Signed-off-by: Hugh Dickins <hugh@veritas.com>
    >> Looks good
    >>
    >> Reviewed-by: Mel Gorman <mel@csn.ul.ie>
    >
    > Thanks.
    >
    >> As I was looking there, it seemed that alloc_large_system_hash() should be
    >> using alloc_pages_exact() instead of having its own "give back the spare
    >> pages at the end of the buffer" logic. If alloc_pages_exact() was used, then
    >> the check for an order >= MAX_ORDER can be pushed down to alloc_pages_exact()
    >> where it may catch other unwary callers.
    >>
    >> How about adding the following patch on top of yours?
    >
    > Well observed, yes indeed. In fact, it even looks as if, shock horror,
    > alloc_pages_exact() was _plagiarized_ from alloc_large_system_hash().
    > Blessed be the GPL, I'm sure we can skip the lengthy lawsuits!

    As a matter of fact, I was planning to call my lawyer, so I'll reconsider
    this and save some euros, thanks !

    ;)

    It makes sense to use a helper function if it already exist, of course !

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