Linux-f2fs-devel Archive on lore.kernel.org
 help / color / Atom feed
From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: ecryptfs@vger.kernel.org, "Theodore Y. Ts'o" <tytso@mit.edu>,
	linux-kernel@vger.kernel.org,
	Matthew Wilcox <willy@infradead.org>,
	Tyler Hicks <tyhicks@canonical.com>,
	Eric Biggers <ebiggers@kernel.org>,
	linux-fscrypt@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, Jaegeuk Kim <jaegeuk@kernel.org>,
	linux-f2fs-devel@lists.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH] fs: introduce is_dot_dotdot helper for cleanup
Date: Mon, 2 Dec 2019 18:39:54 -0800
Message-ID: <20191203023954.GB7323@magnolia> (raw)
In-Reply-To: <357ad021-a58c-ad46-42bd-d5012126276f@loongson.cn>

On Tue, Dec 03, 2019 at 10:07:41AM +0800, Tiezhu Yang wrote:
> On 12/03/2019 04:03 AM, Matthew Wilcox wrote:
> > On Mon, Dec 02, 2019 at 06:10:13PM +0800, Tiezhu Yang wrote:
> > > There exists many similar and duplicate codes to check "." and "..",
> > > so introduce is_dot_dotdot helper to make the code more clean.
> > The idea is good.  The implementation is, I'm afraid, badly chosen.
> > Did you benchmark this change at all?  In general, you should prefer the
> > core kernel implementation to that of some less-interesting filesystems.
> > I measured the performance with the attached test program on my laptop
> > (Core-i7 Kaby Lake):
> > 
> > qstr . time_1 0.020531 time_2 0.005786
> > qstr .. time_1 0.017892 time_2 0.008798
> > qstr a time_1 0.017633 time_2 0.003634
> > qstr matthew time_1 0.011820 time_2 0.003605
> > qstr .a time_1 0.017909 time_2 0.008710
> > qstr , time_1 0.017631 time_2 0.003619
> > 
> > The results are quite stable:
> > 
> > qstr . time_1 0.021137 time_2 0.005780
> > qstr .. time_1 0.017964 time_2 0.008675
> > qstr a time_1 0.017899 time_2 0.003654
> > qstr matthew time_1 0.011821 time_2 0.003620
> > qstr .a time_1 0.017889 time_2 0.008662
> > qstr , time_1 0.017764 time_2 0.003613
> > 
> > Feel free to suggest some different strings we could use for testing.
> > These seemed like interesting strings to test with.  It's always possible
> > I've messed up something with this benchmark that causes it to not
> > accurately represent the performance of each algorithm, so please check
> > that too.
> 
> [Sorry to resend this email because the mail list server
> was denied due to it is not plain text.]
> 
> Hi Matthew,
> 
> Thanks for your reply and suggestion. I measured the
> performance with the test program, the following
> implementation is better for various of test cases:
> 
> bool is_dot_dotdot(const struct qstr *str)
> {
>         if (unlikely(str->name[0] == '.')) {
>                 if (str->len < 2 || (str->len == 2 && str->name[1] == '.'))
>                         return true;
>         }
> 
>         return false;
> }
> 
> I will send a v2 patch used with this implementation.

Can you make it a static inline since it's such a short function?

--D

> Thanks,
> 
> Tiezhu Yang
> 
> > 
> > > +bool is_dot_dotdot(const struct qstr *str)
> > > +{
> > > +	if (str->len == 1 && str->name[0] == '.')
> > > +		return true;
> > > +
> > > +	if (str->len == 2 && str->name[0] == '.' && str->name[1] == '.')
> > > +		return true;
> > > +
> > > +	return false;
> > > +}
> > > +EXPORT_SYMBOL(is_dot_dotdot);
> > > diff --git a/fs/namei.c b/fs/namei.c
> > > index 2dda552..7730a3b 100644
> > > --- a/fs/namei.c
> > > +++ b/fs/namei.c
> > > @@ -2458,10 +2458,8 @@ static int lookup_one_len_common(const char *name, struct dentry *base,
> > >   	if (!len)
> > >   		return -EACCES;
> > > -	if (unlikely(name[0] == '.')) {
> > > -		if (len < 2 || (len == 2 && name[1] == '.'))
> > > -			return -EACCES;
> > > -	}
> > > +	if (unlikely(is_dot_dotdot(this)))
> > > +		return -EACCES;
> > >   	while (len--) {
> > >   		unsigned int c = *(const unsigned char *)name++;
> 


_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel

  reply index

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-02 10:10 Tiezhu Yang
     [not found] ` <20191202200302.GN20752@bombadil.infradead.org>
2019-12-03  2:07   ` Tiezhu Yang
2019-12-03  2:39     ` Darrick J. Wong [this message]
2019-12-03  8:33       ` Tiezhu Yang
2019-12-03  2:46     ` Matthew Wilcox
2019-12-04 13:06     ` Jean-Louis Biasini via Linux-f2fs-devel

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191203023954.GB7323@magnolia \
    --to=darrick.wong@oracle.com \
    --cc=ebiggers@kernel.org \
    --cc=ecryptfs@vger.kernel.org \
    --cc=jaegeuk@kernel.org \
    --cc=linux-f2fs-devel@lists.sourceforge.net \
    --cc=linux-fscrypt@vger.kernel.org \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=tyhicks@canonical.com \
    --cc=tytso@mit.edu \
    --cc=viro@zeniv.linux.org.uk \
    --cc=willy@infradead.org \
    --cc=yangtiezhu@loongson.cn \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-f2fs-devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-f2fs-devel/0 linux-f2fs-devel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-f2fs-devel linux-f2fs-devel/ https://lore.kernel.org/linux-f2fs-devel \
		linux-f2fs-devel@lists.sourceforge.net
	public-inbox-index linux-f2fs-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/net.sourceforge.lists.linux-f2fs-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git