linux-kernel - Re: [PATCH] hugetlbfs read() support

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Message-ID: <20070719170759.GE2083@us.ibm.com>
Date:	Thu, 19 Jul 2007 10:07:59 -0700
From:	Nishanth Aravamudan <nacc@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Badari Pulavarty <pbadari@...ibm.com>,
	Bill Irwin <bill.irwin@...cle.com>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Nick Piggin <nickpiggin@...oo.com.au>
Subject: Re: [PATCH] hugetlbfs read() support

On 19.07.2007 [09:58:50 -0700], Andrew Morton wrote:
> On Thu, 19 Jul 2007 08:51:49 -0700 Badari Pulavarty <pbadari@...ibm.com> wrote:
> 
> > > > +		}
> > > > +
> > > > +		offset += ret;
> > > > +		retval += ret;
> > > > +		len -= ret;
> > > > +		index += offset >> HPAGE_SHIFT;
> > > > +		offset &= ~HPAGE_MASK;
> > > > +
> > > > +		page_cache_release(page);
> > > > +		if (ret == nr && len)
> > > > +			continue;
> > > > +		goto out;
> > > > +	}
> > > > +out:
> > > > +	return retval;
> > > > +}
> > > 
> > > This code doesn't have all the ghastly tricks which we deploy to
> > > handle concurrent truncate.
> > 
> > Do I need to ? Baaahh!!  I don't want to deal with them. 
> 
> Nick, can you think of any serious consequences of a read/truncate
> race in there?  I can't..
> 
> > All I want is a simple read() to get my oprofile working.  Please
> > advise.
> 
> Did you consider changing oprofile userspace to read the executable
> with mmap?

It's not actually oprofile's code, though, it's libbfd (used by
oprofile). And it works fine (presumably) for other binaries. Just not
for libhugetlbfs-relinked binaries because hugetlbfs doesn't behave like
a normal ramfs (perhaps it shouldn't, but that's a different argument).

But I do think a second reason to do this is to make hugetlbfs behave
like a normal fs -- that is read(), write(), etc. work on files in the
mountpoint. But that is simply my opinion.

Thanks,
Nish

-- 
Nishanth Aravamudan <nacc@...ibm.com>
IBM Linux Technology Center
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