From mboxrd@z Thu Jan 1 00:00:00 1970 From: Johannes Sixt Subject: Re: [PATCH 2/3] mmap(win32): avoid copy-on-write when it is unnecessary Date: Tue, 26 Apr 2016 20:53:23 +0200 Message-ID: <571FB923.9040808@kdbg.org> References: <3e2a45e60e2905f52f962604cf19a0e5e39b9b1b.1461335463.git.johannes.schindelin@gmx.de> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Cc: Junio C Hamano , git@vger.kernel.org, Sven Strickroth To: Johannes Schindelin X-From: git-owner@vger.kernel.org Tue Apr 26 20:53:38 2016 Return-path: Envelope-to: gcvg-git-2@plane.gmane.org Received: from vger.kernel.org ([209.132.180.67]) by plane.gmane.org with esmtp (Exim 4.69) (envelope-from ) id 1av876-0007aB-Bo for gcvg-git-2@plane.gmane.org; Tue, 26 Apr 2016 20:53:36 +0200 Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752749AbcDZSx2 (ORCPT ); Tue, 26 Apr 2016 14:53:28 -0400 Received: from bsmtp1.bon.at ([213.33.87.15]:18027 "EHLO bsmtp1.bon.at" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752616AbcDZSx1 (ORCPT ); Tue, 26 Apr 2016 14:53:27 -0400 Received: from dx.site (unknown [93.83.142.38]) by bsmtp1.bon.at (Postfix) with ESMTPSA id 3qvXKw2YHqz5tlB; Tue, 26 Apr 2016 20:53:24 +0200 (CEST) Received: from [IPv6:::1] (localhost [IPv6:::1]) by dx.site (Postfix) with ESMTP id A6DD8524D; Tue, 26 Apr 2016 20:53:23 +0200 (CEST) User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.7.0 In-Reply-To: <3e2a45e60e2905f52f962604cf19a0e5e39b9b1b.1461335463.git.johannes.schindelin@gmx.de> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org Archived-At: Am 22.04.2016 um 16:31 schrieb Johannes Schindelin: > Often we are mmap()ing read-only. In those cases, it is wasteful to map in > copy-on-write mode. Even worse: it can cause errors where we run out of > space in the page file. > > So let's be extra careful to map files in read-only mode whenever > possible. > > Signed-off-by: Johannes Schindelin > --- > compat/win32mmap.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/compat/win32mmap.c b/compat/win32mmap.c > index 3a39f0f..b836169 100644 > --- a/compat/win32mmap.c > +++ b/compat/win32mmap.c > @@ -22,14 +22,15 @@ void *git_mmap(void *start, size_t length, int prot, int flags, int fd, off_t of > die("Invalid usage of mmap when built with USE_WIN32_MMAP"); > > hmap = CreateFileMapping((HANDLE)_get_osfhandle(fd), NULL, > - PAGE_WRITECOPY, 0, 0, NULL); > + prot == PROT_READ ? PAGE_READONLY : PAGE_WRITECOPY, 0, 0, NULL); As long as we use this implementation with MAP_PRIVATE, PAGE_WRITECOPY is the right setting. Should we insert a check for MAP_PRIVATE to catch unexpected use-cases (think of the index-helper daemon effort)? > > if (!hmap) { > errno = EINVAL; > return MAP_FAILED; > } > > - temp = MapViewOfFileEx(hmap, FILE_MAP_COPY, h, l, length, start); > + temp = MapViewOfFileEx(hmap, prot == PROT_READ ? > + FILE_MAP_READ : FILE_MAP_COPY, h, l, length, start); Same here: FILE_MAP_COPY is the right choice for MAP_SHARED mmaps. > > if (!CloseHandle(hmap)) > warning("unable to close file mapping handle"); > Except for these mental notes, I've no comments on this series. Looks good. -- Hannes