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
