Re: [openib-general] Re: [PATCH][RFC][0/4] InfiniBand userspace verbs implementation

From: Andrew Morton (akpm_at_osdl.org)
Date: 04/26/05

  • Next message: Juergen Quade: "Re: system-freeze: kprobe and do_gettimeofday" 
    Date:	Tue, 26 Apr 2005 12:28:50 -0700
To: Roland Dreier <roland@topspin.com>

    Roland Dreier <roland@topspin.com> wrote:
    >
    > Libor> Do you mean that the set/clear parameters to do_mlock()
    > Libor> are the actual flags which are set/cleared by the caller?
    > Libor> Also, the issue remains that the flags are not reference
    > Libor> counted which is a problem if you are dealing with
    > Libor> overlapping memory region, or even if one region ends and
    > Libor> another begins on the same page. Since the desire is to be
    > Libor> able to pin any memory that a user can malloc this is a
    > Libor> likely scenario.
    >
    > Good point... we need to figure out how to handle:
    >
    > a) app registers 0x0000 through 0x17ff
    > b) app registers 0x1800 through 0x2fff
    > c) app unregisters 0x0000 through 0x17ff
    > d) the page at 0x1000 must stay pinned

    The userspace library should be able to track the tree and the overlaps,
    etc. Things might become interesting when the memory is MAP_SHARED
    pagecache and multiple independent processes are involved, although I guess
    that'd work OK.

    But afaict the problem wherein part of a page needs VM_DONTCOPY and the
    other part does not cannot be solved.

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