Messages in this thread | | | Date | Wed, 28 Jun 2023 15:12:10 -0300 | Subject | Re: [PATCH] pstore: ramoops: support pmsg size larger than kmalloc limitation | From | "Guilherme G. Piccoli" <> |
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On 28/06/2023 19:10, Yuxiao Zhang wrote: > Thanks for reviewing the patch. > > On 28 Jun 2023 07:30:16 +0200, Greg KH wrote: >> What is that max size? > > The max size is arch dependent, it should be 2^(PAGE_SIZE+MAX_ORDER). In our environment it is 4M. > >> what in-kernel user is hitting this in the pstore implementation? > > We are trying to use pmsg to hold a core dump file, so we have pmsg-size=32M and thus hit this issue. > > Other than us, here is one I found that trying to save dmesg beyond kmalloc limitaton: > https://lore.kernel.org/lkml/b2d66d9f-15a6-415c-2485-44649027a1d5@igalia.com/T/
Hi Yuxiao Zhang, thanks for the improvement! And also, thanks for mentioning the thread above - I tested your patch today and was soon to write you this message heh
So, first of all, the patch works for the Steam Deck case - kernel 6.4 with or without your patch behaved the same, i.e., pstore/ramoops worked and it was possible to collect the dmesg.
But when I tried to increase the record size in ramoops, I got this error: https://termbin.com/b12e
This is the same error as mentioned in the thread above. And it happens when I try to bump the record size to 4MB, the biggest working value is still 2MB. Maybe a missing spot, which remained using kmalloc() instead of the virtual variant?
Also - Kees certainly knows that way better, but - are we 100% sure that the region for pstore can be non-contiguous? For some reason, I always thought this was a requirement - grepping the code, I found this (wrong?) comment: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/fs/pstore/zone.c#n3
Cheers,
Guilherme
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