linux-kernel - Re: [PATCH v5 2/6] fs/dcache: Make negative dentry tracking configurable

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Date:   Mon, 2 Jul 2018 14:12:06 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jan Kara <jack@...e.cz>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Ingo Molnar <mingo@...nel.org>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Larry Woodman <lwoodman@...hat.com>,
        James Bottomley <James.Bottomley@...senPartnership.com>,
        "Wangkai (Kevin C)" <wangkai86@...wei.com>
Subject: Re: [PATCH v5 2/6] fs/dcache: Make negative dentry tracking
 configurable

On Mon,  2 Jul 2018 13:51:59 +0800 Waiman Long <longman@...hat.com> wrote:

> The negative dentry tracking is made a configurable option so that
> users who don't care about negative dentry tracking will have the
> option to disable it. The new config option DCACHE_TRACK_NEG_ENTRY
> is disabled by default.
> 
> If this option is enabled, a new kernel parameter "neg_dentry_pc=<%>"
> allows users to set the soft limit on how many negative dentries are
> allowed as a percentage of the total system memory. The default is 2%
> and this new parameter accept a range of 0-10% where 0% means there
> is no limit.
> 
> When the soft limit is reached, a warning message will be printed to
> the console to alert the system administrator.

It would be much more convenient if this was tunable at runtime via yet
another /proc knob.  Is there any particular reason why we can't do this?