linux-kernel - Re: [PATCH/RFC] VFS: don't keep disconnected dentries on d

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Message-ID: <87vah1j8m3.fsf@notabene.neil.brown.name>
Date:   Thu, 21 Dec 2017 10:13:40 +1100
From:   NeilBrown <neilb@...e.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "J. Bruce Fields" <bfields@...ldses.org>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        Anna Schumaker <Anna.Schumaker@...app.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Linux NFS Mailing List <linux-nfs@...r.kernel.org>
Subject: Re: [PATCH/RFC] VFS: don't keep disconnected dentries on d_anon

On Wed, Dec 20 2017, Matthew Wilcox wrote:

> On Thu, Dec 21, 2017 at 09:45:40AM +1100, NeilBrown wrote:
>> -c/ Helper routines to allocate anonymous dentries, and to help attach
>> +   prefix.  If the refcount on a dentry with this flag set
>> +   becomes zero, the dentry is immediately discarded, rather than being
>> +   kept in the dcache.  If a dentry that is not already in the dcache
>> +   is repeatedly accessed by filehandle (as NFSD might do), an new dentry
>> +   will be a allocated for each access, and discarded at the end of
>
> s/a //
>
>> +   the access.  As there is no parent, children, or name in the dentry
>> +   is it unlikely that there will be any useful information to lose,
>> +   and allocating a new dentry should normally be fast.
>
> How about:
>
> As the dentry is completely unattached, there is little information to
> lose, and allocating a new dentry is normally fast.

Yes, that is less verbose, and probably just as informative.
Every time I rehearse this argument I wonder about d_fsdata.
I don't think it is actually relevant, but I feel that by not mentioning
it, I'm being dishonest...  Maybe I should think of it as being "less
distracting".

Thanks - if this gets far enough to deserve a resent, I'll add those
changes.

NeilBrown

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