Messages in this thread | | | Date | Fri, 26 Nov 2021 17:39:45 +0800 | From | Peter Xu <> | Subject | Re: [PATCH] mm: split thp synchronously on MADV_DONTNEED |
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On Fri, Nov 26, 2021 at 10:16:58AM +0100, David Hildenbrand wrote: > Would this really apply to MADV_DONTNEED on shmem, and would deferred > splitting apply on shmem? I'm constantly confused about shmem vs. anon, > but I would have assumed that shmem is fd-based and we wouldn't end up > in rmap_walk_anon. For shmem, the pagecache would contain the THP which > would stick around and deferred splits don't even apply.
Good point.. when split on shmem we just clear pmd, so yeah I don't think we'll ever add it into the deferred list.
> User space can trigger a split manually using some MADV hackery. But it > can only be used for the use case here, where we actually want to zap a > page. > > 1. MADV_FREE a single 4k page in the range. This will split the PMD->PTE > and the compound page.
Seems to be a very implicit but working solution indeed.
> 2. MADV_DONTNEED either the complete range or the single 4k page.
Is this what this patch is working on?
Thanks,
-- Peter Xu
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