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    SubjectRe: [RFC][PATCH] PM: Force GFP_NOIO during suspend/resume (was: Re: [linux-pm] Memory allocations in .suspend became very unreliable)
    Date
    On Monday 18 January 2010, KOSAKI Motohiro wrote:
    > > Hi,
    > >
    > > I thing the snippet below is a good summary of what this is about.
    > >
    > > On Saturday 16 January 2010, Rafael J. Wysocki wrote:
    > > > On Saturday 16 January 2010, Maxim Levitsky wrote:
    > > > > On Sat, 2010-01-16 at 01:57 +0100, Rafael J. Wysocki wrote:
    > > > > > On Saturday 16 January 2010, Maxim Levitsky wrote:
    > > > > > > On Fri, 2010-01-15 at 23:03 +0100, Rafael J. Wysocki wrote:
    > > > > > > > On Friday 15 January 2010, Maxim Levitsky wrote:
    > > > > > > > > Hi,
    > > > > > > >
    > > > > > > > Hi,
    > > > > > > >
    > > > > > > > > I know that this is very controversial, because here I want to describe
    > > > > > > > > a problem in a proprietary driver that happens now in 2.6.33-rc3
    > > > > > > > > I am taking about nvidia driver.
    > > > > > > > >
    > > > > > > > > Some time ago I did very long hibernate test and found no errors after
    > > > > > > > > more that 200 cycles.
    > > > > > > > >
    > > > > > > > > Now I update to 2.6.33 and notice that system will hand when nvidia
    > > > > > > > > driver allocates memory is their .suspend functions.
    > > > > > > >
    > > > > > > > They shouldn't do that, there's no guarantee that's going to work at all.
    > > > > > > >
    > > > > > > > > This could fail in 2.6.32 if I would run many memory hungry
    > > > > > > > > applications, but now this happens with most of memory free.
    > > > > > > >
    > > > > > > > This sounds a little strange. What's the requested size of the image?
    > > > > > > Don't know, but system has to be very tight on memory.
    > > > > >
    > > > > > Can you send full dmesg, please?
    > > > >
    > > > > I deleted it, but for this case I think that hang was somewhere else.
    > > > > This task was hand on doing forking, which probably happened even before
    > > > > the freezer.
    > > > >
    > > > > Anyway, the problem is clear. Now __get_free_pages blocks more often,
    > > > > and can block in .suspend even if there is plenty of memory free.
    > >
    > > This is suspicious, but I leave it to the MM people for consideration.
    > >
    > > > > I now patched nvidia to use GFP_ATOMIC _always_, and problem disappear.
    > > > > It isn't such great solution when memory is tight though....
    > > > >
    > > > > This is going to hit hard all nvidia users...
    > > >
    > > > Well, generally speaking, no driver should ever allocate memory using
    > > > GFP_KERNEL in its .suspend() routine, because that's not going to work, as you
    > > > can readily see. So this is a NVidia bug, hands down.
    > > >
    > > > Now having said that, we've been considering a change that will turn all
    > > > GFP_KERNEL allocations into GFP_NOIO during suspend/resume, so perhaps I'll
    > > > prepare a patch to do that and let's see what people think.
    > >
    > > If I didn't confuse anything (which is likely, because it's a bit late here
    > > now), the patch below should do the trick. I have only checked that it doesn't
    > > break compilation, so please take it with a grain of salt.
    > >
    > > Comments welcome.
    >
    > Hmm..
    > I don't think this is good idea.
    >
    > GFP_NOIO mean "Please don't reclaim if the page is dirty". It mean the system
    > have lots dirty pages, this patch might makes hung up.

    The point is to prevent the mm subsystem from using I/O. If there's a better
    way, please tell me. :-)

    > If suspend need lots memory, we need to make free memory before starting IO
    > suspending, I think.

    Suspend as such doesn't need a lot of memory, except for some drivers doing
    things they shouldn't do.

    However, there are a few problems that need to be addressed in general.

    First, we can't really guarantee that there's a lot of free memory available
    during suspend and some memory allocations are done indirectly, using
    GFP_KERNEL (for example, when new kernel threads are started). If one of
    these is done during suspend and it happens to cause the mm subsystem to
    start I/O on a suspended devices, the kernel will lock up.

    Second, there may be a memory allocation in progress when suspend is started
    that causes I/O to happen and races with the suspend process. If the latter
    wins the race, the I/O may be attempted on a suspended device and the kernel
    will lock up.

    My patch attempts to avoid these two problems as well as the problem with
    drivers using GFP_KERNEL allocations during suspend which I admit might be
    solved by reworking the drivers.

    Thanks,
    Rafael


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