From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Xu Subject: Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared memory types Date: Mon, 30 May 2022 12:00:52 -0400 Message-ID: References: <20220527193936.30678-1-peterx@redhat.com> <33fd4731-9765-d78b-bdc3-f8243c98e81f@linux.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=6fQFZKIn0aAHsEt/geMh3vNufZ47+6R+BsKfdpfiy3g=; b=dnbF/2e2g91Eqr mgNZYghPrUYP+R9PAvuq+AV2PH8A1wCQKk0UMKLGHxa0S7y8R2TNZoPai8E+LzxbnLSbFc92GR7jH E+kioaxFU2kKoD575eei11bnmIP8oaRGtmN6VOYpstSfOPx/02Rgo93VbpfiDFoRTQHPoELMye9Z6 yqO6c3QzWWIuVU4Az71f3McpWNDApigETclemzMbUYUA2nPr5SZwRJ5A8rJheEXJoxgTLWdQzMc6E H/UJA7JqcazeVw9/1ngewLcQLAwl04EjgsLaK4P5MJNLf4zMN3I4mrbFCFdMFHhOuRCqJZwNAUjPA 0i/iz1LdIfeGDrFrLxRQ==; DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1653926460; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=9ZWphZRcK3afyDhn+H8+iYAM34Y/wtF11YrAt0KXpqo=; b=OAlzTeE5V8IDemnaydPys11/ZrVI/qBW1DOX6CPplb5qXISrVW1Skgh7NUzAUpdX2Yqw/p pHKMJG+8Mdx/ufIWFXE5y5I8riDML3OEKL/xpQCxyErsRfUKjW22PRJZPOar4KJ4zfDQ61 nAJEfPCcXlXGS1LH0+N1yZAXk2j7fts= In-Reply-To: Content-Disposition: inline List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-riscv" Errors-To: linux-riscv-bounces+glpr-linux-riscv=m.gmane-mx.org@lists.infradead.org To: Christian Borntraeger Cc: Heiko Carstens , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Will Deacon , Matt Turner , linux-s390@vger.kernel.org, Andrew Morton , Brian Cain , Borislav Petkov , linux-alpha@vger.kernel.org, Alistair Popple , Jonas Bonn , linux-arm-kernel@lists.infradead.org, linux-ia64@vger.kernel.org, Michael Ellerman , Stefan Kristiansson , linux-snps-arc@lists.infradead.org, Vineet Gupta , Vasily Gorbik , Vlastimil Babka , Ivan Kokshaysky , Rich Felker , sparclinux@vger.kernel.org, Russell King , David Hildenbrand , Benjamin On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote: > On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote: > > > > > > Am 29.05.22 um 22:33 schrieb Heiko Carstens: > > [...] > > > > > > Guess the patch below on top of your patch is what we want. > > > Just for clarification: if gmap is not NULL then the process is a kvm > > > process. So, depending on the workload, this optimization makes sense. > > > > > > diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c > > > index 4608cc962ecf..e1d40ca341b7 100644 > > > --- a/arch/s390/mm/fault.c > > > +++ b/arch/s390/mm/fault.c > > > @@ -436,12 +436,11 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access) > > > /* The fault is fully completed (including releasing mmap lock) */ > > > if (fault & VM_FAULT_COMPLETED) { > > > - /* > > > - * Gmap will need the mmap lock again, so retake it. TODO: > > > - * only conditionally take the lock when CONFIG_PGSTE set. > > > - */ > > > - mmap_read_lock(mm); > > > - goto out_gmap; > > > + if (gmap) { > > > + mmap_read_lock(mm); > > > + goto out_gmap; > > > + } > > > + goto out; Hmm, right after I replied I found "goto out" could be problematic, since all s390 callers of do_exception() will assume it an error condition (side note: "goto out_gmap" contains one step to clear "fault" to 0). I'll replace this with "return 0" instead if it looks good to both of you. I'll wait for a confirmation before reposting. Thanks, -- Peter Xu