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Date: Thu, 12 Apr 2007 04:37:12 +0200 From: Jörn Engel <joern@...ybastard.org> To: Neil Brown <neilb@...e.de> Cc: Theodore Tso <tytso@....edu>, "H. Peter Anvin" <hpa@...or.com>, Christoph Hellwig <hch@...radead.org>, Ulrich Drepper <drepper@...il.com>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: If not readdir() then what? On Thu, 12 April 2007 11:46:41 +1000, Neil Brown wrote: > > I could argue that nfs came before ext3+dirindex, so ext3 should have > been designed to work properly with NFS. You could argue that fixing > it in nfsd fixes it for all filesystems. But I'm not sure either of > those arguments are likely to be at all convincing... Caring about a non-ext3 filesystem, I sure would like an nfs solution as well. :) > Hmmm. I wonder. Which is more likely? > - That two 64bit hashes from some set are the same > - or that 65536 48bit hashes from a set of equal size are the same. The former. Each bit going from hash strength to collision chain length reduces the likelihood of an overflow. In the extreme case of a 0bit hash and 64bit collision chain, you need 2^64 entries compared to 2^32 for the other extreme. However, the collision chain gives me quite a bit of headache. One would have to store each entry's position on the chain, deal with older entries getting deleted, newer entries getting removed, etc. All this requires a lot of complicated code that basically never gets tested in the wild. Just settling for a 64bit hash and returning -EEXIST when someone causes a collision an creat() sounds more appealing. Directories with 4 billion entries will cause problems, but that is hardly news to anyone. Jörn -- Fantasy is more important than knowledge. Knowledge is limited, while fantasy embraces the whole world. -- Albert Einstein - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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