On 03/25/2013 01:42 AM, Minchan Kim wrote:
On Fri, Mar 22, 2013 at 10:06:56AM -0700, John Stultz wrote:
So, if I understand you properly, its more an issue of the the added
cost of making the purged range non-volatile, and re-faulting in the
pages if we purge them all, when we didn't actually have the memory
pressure to warrant purging the entire range? Hrm. Ok, I can sort of
see that. So if we do partial-purging, all the data in the range is
invalid - since we don't know which pages in particular were purged,
but the costs when marking the range non-volatile and the costs of
over-writing the pages with the re-created data will be slightly
cheaper.
It could be heavily cheaper with my experiment in this patchset.
Allocator could avoid minor fault from 105799867 to 9401.
I guess the other benefit is if you're using the SIGBUS semantics,
you might luck out and not actually touch a purged page. Where as if
the entire range is purged, the process will definitely hit the
SIGBUS if its accessing the volatile data.
Yes. I guess that's why Taras liked it.
Quote from old version
"
4) Having a new system call makes it easier for userspace apps to
detect kernels without this functionality.
I really like the proposed interface. I like the suggestion of having
explicit FULL|PARTIAL_VOLATILE. Why not include PARTIAL_VOLATILE as a
required 3rd param in first version with expectation that
FULL_VOLATILE will be added later(and returning some not-supported error
in meantime)?
"
Thanks again for the clarifications on your though process here!
I'm currently trying to rework your patches so we can reuse this for
file data as well as pure anonymous memory. The idea being that we add
one level of indirection: a vrange_root structure, which manages the
root of the rb interval tree as well as the lock. This vrange_root can
then be included in the mm_struct as well as address_space structures
depending on which type of memory we're dealing with. That way most of
the same infrastructure can be used to manage per-mm volatile ranges as
well as per-inode volatile ranges.
Sorting out how to handle vrange() calls that cross both anonymous and
file vmas will be interesting, and may have some of the drawbacks of the
vma based approach, but I think it will still be simpler. To start we
may just be able to require that any vrange() calls don't cross vma
types (possibly using separate syscalls for file and anonymous vranges).
Anyway, that's my current thinkig. You can preview my current attempt here:
http://git.linaro.org/gitweb?p=people/jstultz/android-dev.git;a=shortlog;h=refs/heads/dev/vrange-minchan
Thanks so much again for your moving this work forward!
-john
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