linux-kernel - Re: [patch] epoll use a single inode ...

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Message-Id: <200703071952.13219.dada1@cosmosbay.com>
Date:	Wed, 7 Mar 2007 19:52:13 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Davide Libenzi <davidel@...ilserver.org>,
	Avi Kivity <avi@...o.co.il>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [patch] epoll use a single inode ...


> Not only might memcpy() do a "prefetch for read" on the source for some
> architectures (which in turn may end up being slow for an address that
> isn't in the TLB, like NULL), but you depend on a very much internal

Well, I hope a prefetch(NULL) is OK because we are doing millions of them (see 
include/linux/list.h :) )

> detail, since it *could* have been using something like
>
> 	memcpy(dname, name->name, name->len+1);
>

Yes very true, I will change that and push to Andrew for mm testing

I was thinking about being able to cache the name into the dentry, do you 
think it's worth the pain ? (its not SMP safe for example...)

static char * pipefs_dname(struct dentry *dentry, char *buffer, int buflen)
{
        if (!dentry->d_iname[0])
                snprintf(dentry->d_iname,
			DNAME_INLINE_LEN_MIN,
			"pipe:[%lu]",
			dentry->d_inode->i_ino);
        strlcpy(buffer, dentry->d_iname, buflen);
        return buffer;
}
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