From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6D9C3C77B73 for ; Sat, 6 May 2023 07:03:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229823AbjEFHDv (ORCPT ); Sat, 6 May 2023 03:03:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56954 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229460AbjEFHDu (ORCPT ); Sat, 6 May 2023 03:03:50 -0400 Received: from out-45.mta0.migadu.com (out-45.mta0.migadu.com [91.218.175.45]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2482AAD18 for ; Sat, 6 May 2023 00:03:47 -0700 (PDT) Message-ID: <92595369-f378-b6ac-915f-f046921f1d59@linux.dev> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.dev; s=key1; t=1683356625; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=deTRnT6majvqIcbAA4+aeFpwQgLJ+x+hzmknl6pAYWg=; b=lpXoWT8Rgg5cYt9zL3+V07fUC7Hyok/3z3LrVWFQKpd2sZAfPWoPj+7s6kdUjdGr39ETrP FwAJ7xjCvaHdyiGC/nKrWxRvg7ulpePQJpH7kBSm9/HFfolu4qY2atbbwqYl9zVkexNtWH MAeOoJLJIr73C6FEREQ7R1+zp2fR7T8= Date: Sat, 6 May 2023 15:03:38 +0800 MIME-Version: 1.0 Subject: Re: [fuse-devel] [PATCH] fuse: add a new flag to allow shared mmap in FOPEN_DIRECT_IO mode Content-Language: en-US To: Bernd Schubert , fuse-devel@lists.sourceforge.net Cc: linux-fsdevel@vger.kernel.org, miklos@szeredi.hu References: <20230505081652.43008-1-hao.xu@linux.dev> X-Report-Abuse: Please report any abuse attempt to abuse@migadu.com and include these headers. From: Hao Xu In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Migadu-Flow: FLOW_OUT Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hi Bernd, On 5/5/23 22:39, Bernd Schubert wrote: > > > On 5/5/23 10:16, Hao Xu wrote: >> From: Hao Xu >> >> FOPEN_DIRECT_IO is usually set by fuse daemon to indicate need of strong >> coherency, e.g. network filesystems. Thus shared mmap is disabled since >> it leverages page cache and may write to it, which may cause >> inconsistence. But FOPEN_DIRECT_IO can be used not for coherency but to >> reduce memory footprint as well, e.g. reduce guest memory usage with >> virtiofs. Therefore, add a new flag FOPEN_DIRECT_IO_SHARED_MMAP to allow >> shared mmap for these cases. >> >> Signed-off-by: Hao Xu >> --- >>   fs/fuse/file.c            | 11 ++++++++--- >>   include/uapi/linux/fuse.h |  2 ++ >>   2 files changed, 10 insertions(+), 3 deletions(-) >> >> diff --git a/fs/fuse/file.c b/fs/fuse/file.c >> index 89d97f6188e0..655896bdb0d5 100644 >> --- a/fs/fuse/file.c >> +++ b/fs/fuse/file.c >> @@ -161,7 +161,8 @@ struct fuse_file *fuse_file_open(struct >> fuse_mount *fm, u64 nodeid, >>       } >>         if (isdir) >> -        ff->open_flags &= ~FOPEN_DIRECT_IO; >> +        ff->open_flags &= >> +            ~(FOPEN_DIRECT_IO | FOPEN_DIRECT_IO_SHARED_MMAP); >>         ff->nodeid = nodeid; >>   @@ -2509,8 +2510,12 @@ static int fuse_file_mmap(struct file *file, >> struct vm_area_struct *vma) >>           return fuse_dax_mmap(file, vma); >>         if (ff->open_flags & FOPEN_DIRECT_IO) { >> -        /* Can't provide the coherency needed for MAP_SHARED */ >> -        if (vma->vm_flags & VM_MAYSHARE) >> +        /* Can't provide the coherency needed for MAP_SHARED. >> +         * So disable it if FOPEN_DIRECT_IO_SHARED_MMAP is not >> +         * set, which means we do need strong coherency. >> +         */ >> +        if (!(ff->open_flags & FOPEN_DIRECT_IO_SHARED_MMAP) && >> +            vma->vm_flags & VM_MAYSHARE) >>               return -ENODEV; >>             invalidate_inode_pages2(file->f_mapping); >> diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h >> index 1b9d0dfae72d..003dcf42e8c2 100644 >> --- a/include/uapi/linux/fuse.h >> +++ b/include/uapi/linux/fuse.h >> @@ -314,6 +314,7 @@ struct fuse_file_lock { >>    * FOPEN_STREAM: the file is stream-like (no file position at all) >>    * FOPEN_NOFLUSH: don't flush data cache on close (unless >> FUSE_WRITEBACK_CACHE) >>    * FOPEN_PARALLEL_DIRECT_WRITES: Allow concurrent direct writes on >> the same inode >> + * FOPEN_DIRECT_IO_SHARED_MMAP: allow shared mmap when >> FOPEN_DIRECT_IO is set >>    */ >>   #define FOPEN_DIRECT_IO        (1 << 0) >>   #define FOPEN_KEEP_CACHE    (1 << 1) >> @@ -322,6 +323,7 @@ struct fuse_file_lock { >>   #define FOPEN_STREAM        (1 << 4) >>   #define FOPEN_NOFLUSH        (1 << 5) >>   #define FOPEN_PARALLEL_DIRECT_WRITES    (1 << 6) >> +#define FOPEN_DIRECT_IO_SHARED_MMAP    (1 << 7) > > Thanks, that is what I had in my mind as well. > > I don't have a strong opinion on it (so don't change it before Miklos > commented), but maybe FOPEN_DIRECT_IO_WEAK? Just in case there would > be later on other conditions that need to be weakened? The comment > would say then something like > "Weakens FOPEN_DIRECT_IO enforcement, allows MAP_SHARED mmap" > > Thanks, > Bernd > Hi Bernd, BTW, I have another question: ```   static int fuse_file_mmap(struct file *file, struct vm_area_struct *vma) {           struct fuse_file *ff = file->private_data;           /* DAX mmap is superior to direct_io mmap */           if (FUSE_IS_DAX(file_inode(file)))                   return fuse_dax_mmap(file, vma);           if (ff->open_flags & FOPEN_DIRECT_IO) {                   /* Can't provide the coherency needed for MAP_SHARED */                   if (vma->vm_flags & VM_MAYSHARE)                           return -ENODEV; invalidate_inode_pages2(file->f_mapping);                   return generic_file_mmap(file, vma); }           if ((vma->vm_flags & VM_SHARED) && (vma->vm_flags & VM_MAYWRITE)) fuse_link_write_file(file); file_accessed(file);           vma->vm_ops = &fuse_file_vm_ops;           return 0; } ``` For FOPEN_DIRECT_IO and !FOPEN_DIRECT_IO case, the former set vm_ops to generic_file_vm_ops while the latter set it to fuse_file_vm_ops, and also it does the fuse_link_write_file() stuff. Why is so? What causes the difference here? Thanks, Hao