Messages in this thread |  | | Date | Sun, 3 Sep 2000 01:47:53 -0400 (EDT) | From | Alexander Viro <> |
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On Sat, 2 Sep 2000, Linus Torvalds wrote:
> You don't actually have to be smart. > > There's a really simple way to avoid this: compare the thing you're going > to zero out against zero before you memset() it to zero. If it was already > zero, you just unlock the page and release. > > Downside: you have to read the page in, in order to compare. However, this > turns out to be a non-issue: if there were no blocks on that page (like a > forward truncate) this ends up generating no IO anyway. If there _were_ > blocks on the page, it's likely that one of them was the one we're going > to partially clear anyway, so the "prepare_write()" would have had to read > it in anyway. > > Upside: you don't need to mark it dirty unnecessarily, assuming you just > extended the file. No extra allocation, and no extra write to disk. > > Comments? Basically the "grab_cache_page()" would be a "read_cache_page()" > instead with all the wait-on-page etc stuff.
Works for me. However, that way it looks like a fs/buffer.c fodder. Mind if I just call it block_zero_page(page, from, to) and export it?
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