Messages in this thread |  | | Date | Fri, 25 May 2001 14:24:52 -0400 (EDT) | From | Alexander Viro <> | Subject | Re: DVD blockdevice buffers |
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On Fri, 25 May 2001, Linus Torvalds wrote:
> For example, I suspect that the metadata bitmaps in particular cache so > well that the fact that we need to do several seeks over them every once > in a while is a non-issue: we might be happier having the bitmaps in > memory (and having simpler code), than try to avoid the occasional seeks. > > The "simpler code" argument in particular is, I think, a fairly strong > one. Our current bitmap code is quite horrible, with multiple layers of > caching (ext2 will explicitly hold references to some blocks, while at the > same time depending on the buffer cache to cache the other blocks - > nightmare)
Oh, current code is a complete mess - no arguments here. 8-element LRU. Combined with the fact that directories allocation tries to get even distribution of directory inodes by cylinder groups, you blow that LRU completely on a regular basis if your fs is larger that 16 cg. For 1Kb blocks fs it's 128Mb. For 4Kb - 2Gb. And pain starts at the half of that size.
If you are OK with adding two extra arguments to ->readpage() I could submit a patch replacing that with plain and simple page cache by tomorrow. It should not be a problem to port, but I want to get some sleep before testing it...
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