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SubjectRe: [patch 6/12] hold atomic kmaps across generic_file_read
On Sunday 11 August 2002 00:42, Linus Torvalds wrote:
> For example, what do you do when somebody has a COW-page mapped into it's
> VM space and you want to start paging stuff out?

Clearly it requires a CoW break and swapping out that page won't free any
memory directly, but it will in turn allow the cache page to be dropped. I
suppose your point is that these ideas touch the system in a lot of places,
and right now the code is a little too irregular to withstand lathering on a
new layer of cruft. That's true, but <plug>the reverse mapping work
enables some fundamental VM simplifications that make a lot of things more
local, and so a better base for these new, sophisticated features is on its

> There are "interesting"
> cases that just may mean that doing the COW thing is a really stupid thing
> to do, even if it is intriguing to _think_ about it.

It is good sport, but the real benefits are compelling and will only get more
so. For high end scientific uses (read supercomputing clusters) it's a cinch
developers will prefer high speed file operations that turn in nearly the
same raw performance on large transfers as O_DIRECT while not bypassing the
file cache.

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