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Re: Bug#245678: zsh: built-in rm -rf fills up the memory
- X-seq: zsh-workers 19908
- From: Bart Schaefer <schaefer@xxxxxxxxxxxxxxxx>
- To: zsh-workers@xxxxxxxxxx
- Subject: Re: Bug#245678: zsh: built-in rm -rf fills up the memory
- Date: Mon, 10 May 2004 09:51:53 -0700 (PDT)
- Cc: 245678-submitter@xxxxxxxxxxxxxxx
- In-reply-to: <28310.1084205953@xxxxxxx>
- Mailing-list: contact zsh-workers-help@xxxxxxxxxx; run by ezmlm
- Reply-to: zsh-workers@xxxxxxxxxx
- Sender: schaefer@xxxxxxxxxxxxxxxxxx
On Mon, 10 May 2004, Peter Stephenson wrote:
> This is all ghastly even by zsh standards.
Well, that's what comes of having glued MMAP into the hrealloc() algorithm
piecemeal. Probably what should have been done was just to #ifdef the
entire function body.
> What we should do is the equivalent of realloc as an #else of the code
> above --- mmap a larger chunk, unmap the old one, and return the new
> one.
I think I said that, though I hadn't got so far as to pinpoint where it
needed to happen.
> However, I don't think even *that* is the basic problem. I think this:
>
> old = (old + H_ISIZE - 1) & ~(H_ISIZE - 1);
> new = (new + H_ISIZE - 1) & ~(H_ISIZE - 1);
>
> is wrong --- it should be the heap size here, not H_ISIZE which is
> simply sizeof(union mem_align), which is probably only 4 or 8 words.
It took me a while staring at this to decide that it was doing the right
thing, but I came to the conclusion that it's only actually _wrong_ if
HEAP_ARENA_SIZE is _not_ a multiple of H_ISIZE. And even then I'm pretty
sure "wrong" just means "inefficient".
> We only need to reallocate to heap size boundaries
That's correct, but we _do_ only reallocate to heap size boundaries in the
non-MMAP case. I think. It's only the MMAP'd code, which as I said was
pasted in long after the original algorithm was written, that botches it.
> I might be tempted by proposed solutions involving the complete removal
> of hrealloc.
Which would mean what, exactly? Never grow heap blocks?
(Note that I didn't begin with "why".)
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