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David Alan Gilbert" , "Matthew Wilcox (Oracle)" , Vlastimil Babka , Baolin Wang , Miaohe Lin , Yang Shi , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Queue-Id: 5E6D41C0024 X-Rspamd-Server: rspam01 X-Stat-Signature: zpob7zm6imckdgr8wd5mj7e8kfzfuhrd X-HE-Tag: 1672160586-494030 X-HE-Meta: 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 l4OZJxSH rbS1BM3RAsr5W0XMwViksuLyD3KdUn1ifHU6ReQ0t1OWKYw/0ru+DUA3Muw== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Dec 22, 2022 at 9:30 AM Peter Xu wrote: > > On Wed, Dec 21, 2022 at 08:24:45PM -0500, James Houghton wrote: > > Not sure what the best name for this flag is either. MADV_ENABLE_HGM > > sounds ok. MADV_HUGETLB_HGM or MADV_HUGETLB_SMALL_PAGES could work > > too. No need to figure it out now. > > One more option to consider is MADV_SPLIT (hopefully to be more generic). > > We already decided to reuse thp MADV_COLLAPSE, we can also introduce > MADV_SPLIT and leave thp for later if it can be anything helpful (I > remember we used to discuss this for thp split). > > For hugetlb one SPLIT should enable hgm advise bit on the vma forever. MADV_SPLIT sounds okay to me -- we'll see how it turns out when I send v1. However, there's an interesting API question regarding what address userfaultfd provides. We previously required UFFD_FEATURE_EXACT_ADDRESS when you specified UFFD_FEATURE_MINOR_HUGETLBFS_HGM so that there was no ambiguity. Now, we can do: 1. When MADV_SPLIT is given, userfaultfd will now round addresses to PAGE_SIZE instead of huge_page_size(hstate), and UFFD_FEATURE_EXACT_ADDRESS is not needed. 2. Don't change anything. A user must know to provide UFFD_FEATURE_EXACT_ADDRESS to get the real address, otherwise they get an (unusable) hugepage-aligned address. I think #1 sounds fine; let me know if you disagree. Thanks! - James