linux-kernel - Re: [PATCH v3 0/5] fs/dcache: Limit # of negative dentries

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Date:   Fri, 18 Aug 2017 10:10:17 -0400
From:   Waiman Long <longman@...hat.com>
To:     "Wangkai (Kevin,C)" <wangkai86@...wei.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Jonathan Corbet <corbet@....net>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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>
Subject: Re: [PATCH v3 0/5] fs/dcache: Limit # of negative dentries

On 08/18/2017 05:59 AM, Wangkai (Kevin,C) wrote:
>
>>> In my patch the DCACHE_FILE_REMOVED flag was to distinguish the
>>> removed file and The closed file, I found there was no difference of a
>>> dentry between the removed file and the closed File, they all on the lru list.
>> There is a difference between removed file and closed file. The type field of
>> d_flags will be empty for a removed file which indicate a negative dentry.
>> Anything else is a positive dentry. Look at the inline function d_is_negative()
>> [d_is_miss()] and you will see how it is done.
> After the file was removed, the dentry flag was not MISS, the flag was:
> DCACHE_REFERENCED | DCACHE_RCUACCESS | DCACHE_LRU_LIST | DCACHE_REGULAR_TYPE
> So, the dentry never be freed, until the kernel reclaim the slab memory.

The dentry_unlink_inode() function will clear DCACHE_REGULAR_TYPE.

Cheers,
Longman