Hi

quoted text
> >> "mm: Add min_free_order_shift tunable." seems makes zero sense. I don't think this patch
> >> need to be merge.
> >
> > It makes a marginal amount of sense. Basically what it does is allowing
> > high-order allocations to go much further below their watermarks than is
> > currently allowed. If the platform in question is doing a lot of high-order
> > allocations, this patch could be seen to "fix" the problem but you wouldn't
> > touch mainline with it with a barge pole. It would be more stable to fix
> > the drivers to not use high order allocations or use a mempool.
> 
> The high order allocation that caused problems was the first level
> page table for each process. Each time a new process started the
> kernel would empty the entire page cache to create contiguous free
> memory. With the reserved pageblock mostly full (fixed by the second
> patch) this contiguous memory would then almost immediately get used
> for low order allocations, so the same problem starts again when the
> next process starts. I agree this patch does not fix the problem, but
> it does improve things when the problem hits. I have not seen a device
> in this situation with the second patch applied, but I did not remove
> the first patch in case the reserved pageblock fills up.

I would like to merge the second patch at first. If the same problem still occur, please
post bug report. (and please cc arm folks if it is arm pagetable related)


quoted text
> > It is inconceivable this patch is related to the problem though.
> >
> >> but "mm: Check if any page in a pageblock is reserved before marking it MIGRATE_RESERVE"
> >> treat strange hardware correctly, I think. If Mel ack this, I hope merge it.
> >> Mel, Can we hear your opinion?
> >>
> >
> > This patch is interesting and I am surprised it is required. Is it really the
> > case that page blocks near the start of a zone are dominated with PageReserved
> > pages but the first one happen to be free? I guess it's conceivable on ARM
> > where memmap can be freed at boot time.
> 
> I think this happens by default on arm. The kernel starts at offset
> 0x8000 to leave room for boot parameters, and in recent kernel
> versions (>~2.6.26-29) this memory is freed.
> 
> >
> > There is a theoritical problem with the patch but it is easily resolved.
> > A PFN walker like this must call pfn_valid_within() before calling
> > pfn_to_page(). If they do not, it's possible to get complete garbage
> > for the page and result in a bad dereference. In this particular case,
> > it would be a kernel oops rather than memory corruption though.
> >
> > If that was fixed, I'd see no problem with Acking the patch.
> >
> 
> I can fix this if you want the patch in mainline. I was not sure it
> was acceptable since will slow down boot on all systems, even where it
> is not needed.

bootup code is not fast path. then, small slowdown is ok, I think.
So, I'm looking for your new version patch.



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