Messages in this thread | | | Date | Fri, 11 Mar 2011 17:57:00 +0100 | From | Oleg Nesterov <> | Subject | Re: + x86-mm-handle-mm_fault_error-in-kernel-space.patch added to -mm tree |
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On 03/11, Andrew Vagin wrote: > > On 03/11/2011 02:19 PM, Oleg Nesterov wrote: >> >> Btw, this may be true, but this is irrelevant. If we shouldn't call >> out_of_memory() in this case, then we shouldn't call it at all, even >> if PF_USER. > > Yes. We shouldn't call it at all, even if PF_USER.
Then why did you send this patch? If we should not call it, then we should kill pagefault_out_of_memory() and update the callers instead of adding the special 'if (PF_USER)' checks.
Yes, the current pagefault_out_of_memory() logic looks a bit suspicious, but this needs another discussion. Once again, I am arguing against making it depend on PF_USER, this was my point from the very beginning.
>>> Now pls think what is the >>> difference between these page faults? >> The difference is that oom-killer should free the memory in between. >> _OR_ it can decide to kill us, and _this_ case should be fixed. > > We wait memory in __alloc_pages_may_oom(). I think now handle_mm_fault() > returns VM_FAULT_OOM only if OOM-killer killed current task.
I don't think so, but this doesn't matter.
Once again, if OOM-killer killed current task we do not retry. That is why my patch checks fatal_signal_pending() to fix the bug. That is all.
The point is, if current was _NOT_ killed we should follow the current pagefault_out_of_memory() logic or remove pagefault_out_of_memory() completely.
>> Why do you think the current task should be killed? In this case we >> do not need oom-killer at all, we could always kill the caller of >> alloc_page/etc. > > You don't understand. alloc_page calls oom-killer himself, then try > allocate memory again. Pls look at __alloc_pages_slowpath(). > __alloc_pages_slowpat may fail if order > 3 || gfp_mask & __GFP_NOFAIL > || test_thread_flag(TIF_MEMDIE)
Andrew, please, I know this.
> Probaly you think that oom-killer is called from mm_fault_error() only. > It's incorrect.
And this too ;)
If nothing else. alloc_page doesn't call oom-killer if it is already in progress. At least in this case we should retry after it completes.
Either way, I believe this patch should be dropped.
Oleg.
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