linux-kernel - Re: [PATCH 18/24] netfs: Speed up buffered reading

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Message-ID: <20240802144405.GD2504122@kernel.org>
Date: Fri, 2 Aug 2024 15:44:05 +0100
From: Simon Horman <horms@...nel.org>
To: David Howells <dhowells@...hat.com>
Cc: Christian Brauner <christian@...uner.io>,
	Steve French <smfrench@...il.com>,
	Matthew Wilcox <willy@...radead.org>,
	Jeff Layton <jlayton@...nel.org>,
	Gao Xiang <hsiangkao@...ux.alibaba.com>,
	Dominique Martinet <asmadeus@...ewreck.org>,
	Marc Dionne <marc.dionne@...istor.com>,
	Paulo Alcantara <pc@...guebit.com>,
	Shyam Prasad N <sprasad@...rosoft.com>, Tom Talpey <tom@...pey.com>,
	Eric Van Hensbergen <ericvh@...nel.org>,
	Ilya Dryomov <idryomov@...il.com>, netfs@...ts.linux.dev,
	linux-afs@...ts.infradead.org, linux-cifs@...r.kernel.org,
	linux-nfs@...r.kernel.org, ceph-devel@...r.kernel.org,
	v9fs@...ts.linux.dev, linux-erofs@...ts.ozlabs.org,
	linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 18/24] netfs: Speed up buffered reading

On Fri, Aug 02, 2024 at 03:18:02PM +0100, David Howells wrote:
> Simon Horman <horms@...nel.org> wrote:
> 
> > If the code ever reaches this line, then slice will be used
> > uninitialised below.
> 
> It can't actually happen (or, at least, it shouldn't).  There are only three
> ways of obtaining data: downloading from the server
> (NETFS_DOWNLOAD_FROM_SERVER), reading from the cache (NETFS_READ_FROM_CACHE)
> and just clearing space (NETFS_FILL_WITH_ZEROES); each of those has its own
> if-statement that will set 'slice' or will switch the source to a different
> type that will set 'slice'.
> 
> The problem is that the compiler doesn't know this.
> 
> The check for NETFS_INVALID_READ is there just in case.  Possibly:
> 
> 		if (source == NETFS_INVALID_READ)
> 			break;
> 
> could be replaced with a WARN_ON_ONCE() and an unconditional break.

Thanks, I think that should make the compiler happy without
significantly altering the flow or readability of the code.