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| From: | David Hildenbrand |
| Subject: | Re: [PATCH v4 8/9] migration/ram: Factor out populating pages readable in ram_block_populate_pages() |
| Date: | Fri, 3 Sep 2021 09:58:06 +0200 |
| User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 |
That'll be good enough for live snapshot as uffd-wp works for zero pages, however I'm just afraid it may stop working for some new users of it when zero pages won't suffice.I thought about that as well. But snapshots/migration will read all memory either way and consume real memory when there is no shared zero page. So it's just shifting the point in time when we allocate all these pages I guess.
... thinking again, even when populating on shmem and friends there is nothing stopping pages from getting mapped out again.
What would happen when trying uffd-wp protection on a pte_none() in your current shmem implementation? Will it lookup if there is something in the page cache (not a hole) and set a PTE marker? Or will it simply skip as there is currently nothing in the page table? Or will it simply unconditionally install a PTE marker, even if there is a hole?
Having an uffd-wp mode that doesn't require pre-population would really be great. I remember you shared prototypes.
-- Thanks, David / dhildenb
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