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[99.241.198.116]) by smtp.gmail.com with ESMTPSA id i28-20020a056e021d1c00b002d9037fb02csm412562ila.51.2022.06.23.16.24.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 23 Jun 2022 16:24:32 -0700 (PDT) Date: Thu, 23 Jun 2022 19:24:31 -0400 From: Peter Xu To: Nadav Amit Cc: linux-mm@kvack.org, Nadav Amit , Mike Kravetz , Hugh Dickins , Andrew Morton , Axel Rasmussen , David Hildenbrand , Mike Rapoport Subject: Re: [PATCH v1 2/5] userfaultfd: introduce access-likely mode for common operations Message-ID: References: <20220622185038.71740-1-namit@vmware.com> <20220622185038.71740-3-namit@vmware.com> MIME-Version: 1.0 In-Reply-To: <20220622185038.71740-3-namit@vmware.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1656026676; a=rsa-sha256; cv=none; b=WDa/BooKLXt/Jh+5brzXf1fwIP+mgP2eP25REYr5kkkvQb48jJTUhnN2dVWt92IiJZsR86 8ijzj2nPleaxy/lbs856moDoV/3P7ypVaQQgf3z1tFqN4gubz7q7pJ5EYpc9pHDDGCFQXD HzNjz3bTrsj2tJe05n08bIlDLlxu3c4= ARC-Authentication-Results: i=1; imf08.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=PouVM+cO; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf08.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1656026676; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=slTx64PL6hLKG5y+aPBZKv49No+q//nBHG24bDTZE9U=; b=Ci42GFHVo389bPrDAWLEbVjf95Bz9m1pAiXKi8dCD6/n1A1FXl+hoOyBrDatYM9nlHpRkr pCTx8C0q8uBRMm9NwYBB09XWnv86Z2QNgSbdxlYtV1kMLmyZeOEyze7BxOr+zeueJ+Uzrw yiK5WG/lKnXR/F5PdfVvFAvqcBAOaSQ= X-Stat-Signature: embn4k5ubajs4gj3ua4akjstq9c8pyqk X-Rspamd-Queue-Id: 78C43160027 Authentication-Results: imf08.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=PouVM+cO; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf08.hostedemail.com: domain of peterx@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=peterx@redhat.com X-Rspamd-Server: rspam10 X-Rspam-User: X-HE-Tag: 1656026676-792713 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 Wed, Jun 22, 2022 at 11:50:35AM -0700, Nadav Amit wrote: > From: Nadav Amit > > Using a PTE on x86 with cleared access-bit (aka young-bit) > takes ~600 cycles more than when the access bit is set. At the same > time, setting the access-bit for memory that is not used (e.g., > prefetched) can introduce greater overheads, as the prefetched memory is > reclaimed later than it should be. > > Userfaultfd currently does not set the access-bit (excluding the > huge-pages case). Arguably, it is best to let the user control whether > the access bit should be set or not. The expected use is to request > userfaultfd to set the access-bit when the copy/wp operation is done to > resolve a page-fault, and not to set the access-bit when the memory is > prefetched. > > Introduce UFFDIO_[op]_ACCESS_LIKELY to enable userspace to request the > young bit to be set. > > Cc: Mike Kravetz > Cc: Hugh Dickins > Cc: Andrew Morton > Cc: Axel Rasmussen > Cc: Peter Xu > Cc: David Hildenbrand > Cc: Mike Rapoport > Signed-off-by: Nadav Amit Hmm.. is the hugetlb code overlooked (for both of the hints), or maybe I missed it? Do we need to cover them too? Thanks, -- Peter Xu