Messages in this thread | | | Date | Tue, 18 Feb 2014 10:28:11 -0800 | Subject | Re: [RFC, PATCHv2 0/2] mm: map few pages around fault address if they are in page cache | From | Linus Torvalds <> |
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On Tue, Feb 18, 2014 at 10:07 AM, Kirill A. Shutemov <kirill.shutemov@linux.intel.com> wrote: > > Patch is wrong. Correct one is below.
Hmm. I don't hate this. Looking through it, it's fairly simple conceptually, and the code isn't that complex either. I can live with this.
I think it's a bit odd how you pass both "max_pgoff" and "nr_pages" to the fault-around function, though. In fact, I'd consider that a bug. Passing in "FAULT_AROUND_PAGES" is just wrong, since the code cannot - and in fact *must* not - actually fault in that many pages, since the starting/ending address can be limited by other things.
So I think that part of the code is bogus. You need to remove nr_pages, because any use of it is just incorrect. I don't think it can actually matter, since the max_pgoff checks are more restrictive, but if you think it can matter please explain how and why it wouldn't be a major bug?
Apart from that, I'd really like to see numbers for different ranges of FAULT_AROUND_ORDER, because I think 5 is pretty high, but on the whole I don't find this horrible, and you still lock the page so it doesn't involve any new rules. I'm not hugely happy with another raw radix-tree user, but it's not horrible.
Btw, is the "radix_tree_deref_retry(page) -> goto restart" really necessary? I'd be almost more inclined to just make it just do a "break;" to break out of the loop and stop doing anything clever at all.
IOW, from a quick look there's a couple of small details I don't like that look odd, but ..
Linus
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