On 28.10.20 12:09, Mike Rapoport wrote:
On Tue, Oct 27, 2020 at 09:46:35AM +0100, David Hildenbrand wrote:
On 27.10.20 09:38, Mike Rapoport wrote:
On Mon, Oct 26, 2020 at 06:05:30PM +0000, Edgecombe, Rick P wrote:
Beyond whatever you are seeing, for the latter case of new things
getting introduced to an interface with hidden dependencies... Another
edge case could be a new caller to set_memory_np() could result in
large NP pages. None of the callers today should cause this AFAICT, but
it's not great to rely on the callers to know these details.
A caller of set_memory_*() or set_direct_map_*() should expect a failure
and be ready for that. So adding a WARN to safe_copy_page() is the first
step in that direction :)
I am probably missing something important, but why are we saving/restoring
the content of pages that were explicitly removed from the identity mapping
such that nobody will access them?
Actually, we should not be saving/restoring free pages during
hibernation as there are several calls to mark_free_pages() that should
exclude the free pages from the snapshot. I've tried to find why the fix
that maps/unmaps a page to save it was required at the first place, but
I could not find bug reports.
The closest I've got is an email from Rafael that asked to update
"hibernate: handle DEBUG_PAGEALLOC" patch:
https://lore.kernel.org/linux-pm/200802200133.44098....@sisk.pl/
Could it be that safe_copy_page() tries to workaround a non-existent
problem?
Clould be! Also see
https://lkml.kernel.org/r/38de5bb0-5559-d069-0ce0-daec66ef2...@suse.cz
which restores free page content based on more kernel parameters, not
based on the original content.
--
Thanks,
David / dhildenb
