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Received: from willy by casper.infradead.org with local (Exim 4.98 #2 (Red Hat Linux)) id 1tdcmH-0000000DoV5-0MbZ; Thu, 30 Jan 2025 22:12:49 +0000 Date: Thu, 30 Jan 2025 22:12:48 +0000 From: Matthew Wilcox To: Alexander Gordeev Cc: Gerald Schaefer , Heiko Carstens , Vasily Gorbik , Claudio Imbrenda , Christian Borntraeger , linux-mm@kvack.org Subject: Re: [PATCH] s390: Remove PageDirty check inside mk_pte() Message-ID: References: <20250116212338.653160-1-willy@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: BF20E1C0004 X-Stat-Signature: bfd1tou6ayqenfxnnc7uuki6jegdiz4m X-Rspam-User: X-HE-Tag: 1738275170-991815 X-HE-Meta: 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 lTSA6QYF AcbFbeQ2KX48Yhgh0dScHep9bKC/AppWN81i/rdYpj7YPj/04Sc9ffU9ISxlC5kqkhti0EKvQnCwPNRwMpLobU4rmR7V1jd4aCYzn/WlS0Z2JXtUd5wZE1bkksfyKmjNGrEm5Qw7x783CgpfgsKPcMF/R2V3oESepR99afzRGY/MrtI0bRoRJPCmpRFN3oxzvwxZ+m4lnG5m0ub+6ihQjTFYD9VbKl3dTfuBSlSR9G89x4ICjXqD8mvmF+aAspbCcVndgqUsjoNGgyyCxjh7MAYDY/g== X-Bogosity: Ham, tests=bogofilter, spamicity=0.080326, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Jan 20, 2025 at 05:39:43PM +0100, Alexander Gordeev wrote: > Despite the commit 75edd345e8ed claim above I still observed that a read > access to shmem page could end up in creation of a dirty PTE: > > handle_pte_fault() -> do_pte_missing() -> do_fault() -> > do_read_fault() -> finish_fault() -> set_pte_range() -> mk_pte() > > Our internal discussion (among other things) ended up in a need to really > understand where the faults are coming from. > > Further, a cursory LTP test was showing ~18K page faults increase, which > I did not confirm. That is the first thing I will re-do. > > Whether this change is a pre-requisite for something or what is your aim > wrt to this patch? One of the things that needs to happen for the splitting of struct page and struct folio is the removal of all '&folio->page'. Most are in compatibility code or code that is being transitioned and can safely be ignored. One of the places that needs to be changed is: entry = mk_pte(&folio->page, vma->vm_page_prot); (there's a few places like this). I believe we need a folio_mk_pte(), and I don't want to define it for each architecture. I don't even want to have a default implementation and allow arches to override. So the question becomes whether to: (a) Get rid of the conditional pte_mkdirty() entirely (this trial balloon) (b) Put it in folio_mk_pte() for everybody, not just s390 (c) Put it in set_pte_range() as David suggested. It's feeling like (c) is the best idea.