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Date: Wed, 12 Jun 2019 11:29:27 -0400
From: "J . Bruce Fields" <bfields@fieldses.org>
Subject: Re: [PATCH 1/2] vfs: replace i_readcount with a biased i_count
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To: Amir Goldstein <amir73il@gmail.com>
Cc: Mimi Zohar <zohar@linux.ibm.com>, Miklos Szeredi <miklos@szeredi.hu>, Jeff Layton <jlayton@poochiereds.net>, Al Viro <viro@zeniv.linux.org.uk>, linux-fsdevel <linux-fsdevel@vger.kernel.org>, overlayfs <linux-unionfs@vger.kernel.org>, linux-integrity <linux-integrity@vger.kernel.org>
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On Wed, Jun 12, 2019 at 06:09:59PM +0300, Amir Goldstein wrote:
> But if I am following Miklos' suggestion to make i_count 64bit, inode
> struct size is going to grow for 32bit arch when  CONFIG_IMA is not
> defined, so to reduce impact, I will keep i_readcount as a separate
> member and let it be defined also when BITS_PER_LONG == 64
> and implement inode_is_open_rdonly() using d_count and i_count
> when i_readcount is not defined.

How bad would it be just to let the inode be a little bigger?  How big
is it already on 32 bit architectures?  How much does this change e.g.
how many inodes you can cache per megabyte?

--b.