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Thu, 17 Aug 2023 10:47:06 -0700 (PDT) MIME-Version: 1.0 References: <20230812210053.2325091-1-zokeefe@google.com> In-Reply-To: From: Yang Shi Date: Thu, 17 Aug 2023 10:46:54 -0700 Message-ID: Subject: Re: [EXTERNAL] [PATCH] mm/thp: fix "mm: thp: kill __transhuge_page_enabled()" To: "Zach O'Keefe" Cc: Saurabh Singh Sengar , Matthew Wilcox , Dan Williams , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: CDFD98000D X-Rspam-User: X-Rspamd-Server: rspam02 X-Stat-Signature: nyaxifwc7qwszaphxmot4b1gg9h3augj X-HE-Tag: 1692294427-200741 X-HE-Meta: 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 CTyJj2mr 6DDj+VOKznXckJK8pSGqPqsnSv6GsjWUABWTG/++46jjoX8qVR3eETJHML7wFFvmyloNkVGl7e8xIfCsXtQTVVHmzVrHOf09XSCFn6Q1WXsQE/ejYzfwvGAvHfSK6HUU/+tJZ7MwZEvk23CGNc5gP02dSud7Ka4yq4PhaUf+XmVcwI04jEmSQ6PC4vlUTEdZXUfLIqsUnQ6vq+w/ngnx54RyFzgyUMtTDRSgmxmqeC+hHKMnydnSFUnnNrY4P0wUm+qGV+DFqLiKlt6yp4dwQb02KaBA/BiLWwiFn6hKqsIVtGty8h2zXRGABZYVBYs+4A7Q5ZrQwjZeYDMsBm2nnwsjJNx02PNEqPEuoUCa+XTJCKQ4pUTpK5XTvdROVFKD8veVHURhMhptJhUa296N4kMb1+oq4CCmP7fCcPUbR1FifeBuSp5Cx2y7IEPjlZ6js/X8bj9/oZ4QDCUY= 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, Aug 16, 2023 at 2:48=E2=80=AFPM Zach O'Keefe w= rote: > > > We have a out of tree driver that maps huge pages through a file handle= and > > relies on -> huge_fault. It used to work in 5.19 kernels but 6.1 change= d this > > behaviour. > > > > I don=E2=80=99t think reverting the earlier behaviour of fault_path for= huge pages should > > impact kernel negatively. > > > > Do you think we can restore this earlier behaviour of kernel to allow p= age fault > > for huge pages via ->huge_fault. > > That seems reasonable to me. I think using the existence of a > ->huge_fault() handler as a predicate to return "true" makes sense to > me. The "normal" flow for file-backed memory along fault path still > needs to return "false", so that we correctly fallback to ->fault() > handler. Unless there are objections, I can do that in a v2. Sorry for chiming in late. I'm just back from vacation and trying to catch = up... IIUC the out-of-tree driver tries to allocate huge page and install PMD mapping via huge_fault() handler, but the cleanup of hugepage_vma_check() prevents this due to the check to VM_NO_KHUGEPAGED? So you would like to check whether a huge_fault() handler existed instead of vma_is_dax()?