test9-pre6 and GFP_BUFFER allocations

test9-pre6 and GFP_BUFFER allocations

[Roger Larsson]

Hi,

What will happen in this scenario:
a process
* grabs a fs semaphore
* needs some buffers to do IO, calls __alloc_pages(GFP_BUFFER)
Suppose the system is MIN on free mem, has no inactive_clean pages.
We will end up around line 446 in pages_alloc.c and issue a
try_to_free_pages(...). Then goto try_again.
* In our case this is unlikely to work - not allowed to do IO.
* Will we sleep? Probably not, not even in refill_inactive (no GFP_IO)
  BTW, Why can't we schedule if GFP_IO is not set???
* Will we free any page, to get above MIN - only if there are enough
  clean pages in active list.
* Won't we end up in an infinite loop?
Suppose it does sleep. Will kswapd then be able to free any page
assuming we are holding a critical fs semaphore...

Or am I missing something, again?


One approach could be: only goto try_again if GFP_IO is set.
And alloc one page from the critical memory pool.
I will try this.

/RogerL

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Re: test9-pre6 and GFP_BUFFER allocations

[Ingo Molnar]

On Sat, 23 Sep 2000, Roger Larsson wrote:

> * Won't we end up in an infinite loop?

FYI, i still see a rare deadlock, even under test9-pre6.

	Ingo

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Re: test9-pre6 and GFP_BUFFER allocations

[Ingo Molnar]

On Sat, 23 Sep 2000, Roger Larsson wrote:

> One approach could be: only goto try_again if GFP_IO is set.
> And alloc one page from the critical memory pool.
> I will try this.

i'll try this too.

	Ingo

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