Re: Intermittent storage (dm-crypt?) freeze - regression 6.4->6.5

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On 10/30/23 12:22, Mikulas Patocka wrote:
> 
> 
> On Mon, 30 Oct 2023, Vlastimil Babka wrote:
> 
>> Ah, missed that. And the traces don't show that we would be waiting for
>> that. I'm starting to think the allocation itself is really not the issue
>> here. Also I don't think it deprives something else of large order pages, as
>> per the sysrq listing they still existed.
>> 
>> What I rather suspect is what happens next to the allocated bio such that it
>> works well with order-0 or up to costly_order pages, but there's some
>> problem causing a deadlock if the bio contains larger pages than that?
> 
> Yes. There are many "if (order > PAGE_ALLOC_COSTLY_ORDER)" branches in the 
> memory allocation code and I suppose that one of them does something bad 
> and triggers this bug. But I don't know which one.

It's not what I meant. All the interesting branches for costly order in page
allocator/compaction only apply with __GFP_DIRECT_RECLAIM, so we can't be
hitting those here.
The traces I've seen suggest the allocation of the bio suceeded, and
problems arised only after it was submitted.

I wouldn't even be surprised if the threshold for hitting the bug was not
exactly order > PAGE_ALLOC_COSTLY_ORDER but order > PAGE_ALLOC_COSTLY_ORDER
+ 1 or + 2 (has that been tested?) or rather that there's no exact
threshold, but probability increases with order.

>> Cc Honza. The thread starts here:
>> https://lore.kernel.org/all/ZTNH0qtmint%2FzLJZ@mail-itl/
>> 
>> The linked qubes reports has a number of blocked task listings that can be
>> expanded:
>> https://github.com/QubesOS/qubes-issues/issues/8575
> 
> Mikulas
> 





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