Re: What to expect with the 2.6 VM

From: William Lee Irwin III (
Date: Wed Jul 02 2003 - 18:11:22 EST

On Wed, Jul 02, 2003 at 03:15:51PM -0700, William Lee Irwin III wrote:
>> What complexity? Just unmap it if you can't allocate a pte_chain and
>> park it on the LRU.

On Thu, Jul 03, 2003 at 12:26:41AM +0200, Andrea Arcangeli wrote:
> the complexity in munlock to rebuild what you destroyed in mlock, that's
> linear at best (and for anonymous mappings there's no objrmap, plus
> objrmap isn't even linear but quadratic in its scan [hence the problem
> with it], though in practice it would be normally faster than the linear
> of the page scanning ;)

Computational complexity; okay.

It's not quadratic; at each munlock(), it's not necessary to do
anything more than:

for each page this mlock()'er (not _all_ mlock()'ers) maps of this thing
        grab some pagewise lock
        if pte_chain allocation succeeded
                add pte_chain
                /* you'll need to put anon pages in swapcache in mlock() */
                unmap the page
        decrement lockcount
        if lockcount vanished
        park it on the LRU
        drop the pagewise lock

Individual mappers whose mappings are not mlock()'d add pte_chains when
faulting the things in just like before.

-- wli
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