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    SubjectRe: [linux-pm] [RFD] swsusp problem: Drivers allocate much memory during suspend (was: Re: 2.6.21-rc5: swsusp: Not enough free memory)
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    Hi.

    On Sat, 2007-04-14 at 00:38 +0200, Pavel Machek wrote:
    > Hi!
    >
    > > > > > > Well, it looks like someone allocated about 6000 pages after we had freed
    > > > > > > enough memory for suspending.
    > > > > >
    > > > > > We have a tunable allowance in Suspend2 for this, because fglrx
    > > > > > allocates a lot of pages in its suspend routine if DRI is enabled. I
    > > > > > think some other drivers do too, but fglrx is the main one I know.
    > > > >
    > > > > I wasn't aware of that, thanks for the information.
    > > > >
    > > > > I think this means we'll probably need to add a tunable, similar to image_size,
    > > > > that will allow the users to specify how much spare memory they want to reserve
    > > > > for suspending (instead of the constant PAGES_FOR_IO). IMO we can call it
    > > > > 'spare_memory'.
    > > >
    > > > Just increase PAGES_FOR_IO. This should not be tunable.
    > >
    > > If we don't have a means for drivers to pre-allocate or say how much
    > > memory they need, it should be tunable. Frankly, I'm startled that you
    > > guys haven't heard of this issue before now. I can't believe everyone
    > > who has ever wanted to hibernate with DRM enabled has been using
    > > Suspend2. Maybe this is one of the sources of complaints that swsusp
    > > isn't reliable?
    >
    > We do not support closed-source drivers, and open-source drivers are
    > well behaved.

    I didn't say fglrx was the only example. Any system using DRI (not DRM,
    sorry), would, I think, be expected. I just mention fglrx because I have
    a Radeon 200M that can only use fglrx for Beryl etc at the mo - it's the
    one I'm familiar with.

    > > > > IMO to really fix the problem, we should let the drivers that need much memory
    > > > > for suspending allocate it _before_ the memory shrinker is called. For this
    > > > > purpose we can use notifiers that will be called before we start the shrinking
    > > > > of memory. Namely, if a driver needs to allocate substantial amount
    > > > > of memory
    > > >
    > > > Yes please. Using that notifier without leaking the memory will be
    > > > "interesting" but if someone needs so much memory during suspend, let
    > > > them eat their own complexity.
    > >
    > > It doesn't need to be that complex. Add another (optional) function to
    > > the driver model to let drivers say how much they want and it becomes
    > > trivial. Maybe this idea should be preferred over the notifier chain.
    >
    > Actually, it is trivial to prealocate during boot ;-). As the notifier
    > chain can be useful for other stuff, too, I'd go that way.

    Pavel! Talk sense! You're not seriously suggesting squirreling away 35
    megabytes of a user's memory at boot just because they might want to
    hibernate with DRI enabled later? Yes, 35 megabytes is a realistic
    amount.

    Regards,

    Nigel
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