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Date:   Mon, 10 Jul 2023 21:42:39 -0700
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Subject: Re: [PATCH 5/5] docs: fuse: improve FUSE consistency explanation
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To:     Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>,
        Miklos Szeredi <miklos@szeredi.hu>,
        Jonathan Corbet <corbet@lwn.net>,
        linux-fsdevel@vger.kernel.org, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     me@jcix.top
References: <20230711043405.66256-1-zhangjiachen.jaycee@bytedance.com>
 <20230711043405.66256-6-zhangjiachen.jaycee@bytedance.com>
From:   Randy Dunlap <rdunlap@infradead.org>
In-Reply-To: <20230711043405.66256-6-zhangjiachen.jaycee@bytedance.com>
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Hi--

On 7/10/23 21:34, Jiachen Zhang wrote:
> Signed-off-by: Jiachen Zhang <zhangjiachen.jaycee@bytedance.com>
> ---
>  Documentation/filesystems/fuse-io.rst | 32 +++++++++++++++++++++++++--
>  1 file changed, 30 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/filesystems/fuse-io.rst b/Documentation/filesystems/fuse-io.rst
> index 255a368fe534..cdd292dd2e9c 100644
> --- a/Documentation/filesystems/fuse-io.rst
> +++ b/Documentation/filesystems/fuse-io.rst

> @@ -24,7 +31,8 @@ after any writes to the file.  All mmap modes are supported.
>  The cached mode has two sub modes controlling how writes are handled.  The
>  write-through mode is the default and is supported on all kernels.  The
>  writeback-cache mode may be selected by the FUSE_WRITEBACK_CACHE flag in the
> -FUSE_INIT reply.
> +FUSE_INIT reply. In either modes, if the FOPEN_KEEP_CACHE flag is not set in

                       either mode,

> +the FUSE_OPEN, cached pages of the file will be invalidated immediatedly.

                                                               immediately.

>  
>  In write-through mode each write is immediately sent to userspace as one or more
>  WRITE requests, as well as updating any cached pages (and caching previously
> @@ -38,7 +46,27 @@ reclaim on memory pressure) or explicitly (invoked by close(2), fsync(2) and
>  when the last ref to the file is being released on munmap(2)).  This mode
>  assumes that all changes to the filesystem go through the FUSE kernel module
>  (size and atime/ctime/mtime attributes are kept up-to-date by the kernel), so
> -it's generally not suitable for network filesystems.  If a partial page is
> +it's generally not suitable for network filesystems (you can consider the
> +writeback-cache-v2 mode mentioned latter for them).  If a partial page is

                                     later

>  written, then the page needs to be first read from userspace.  This means, that
>  even for files opened for O_WRONLY it is possible that READ requests will be
>  generated by the kernel.


-- 
~Randy