Re: [PATCH] workaround for lost dirty bits on x86 SMP

[Ben LaHaise <bcrl@redhat.com>]

On Tue, 12 Sep 2000, Stephen C. Tweedie wrote:

> Of course it won't, because you aren't testing the new behaviour!
> Anonymous pages are always dirty, and shared mmaped pages in
> MAP_PRIVATE regions are always clean.  The only place where you need
> to track the dirty bit dynamically is when you use shared writeable
> mmaps --- can you measure a performance change there?

Here's a more realistic test, and yes it does extract a heavy performance
hit -- unpatched read then write to 1 byte of 1GB of pages:

size is 1073741825
addr = 0x4010f000
read fault test: start=29670620301256 stop=29670945360465, elapsed=325059209
write fault test: start=29670945400339 stop=29671024199394, elapsed=78799055

patched:

size is 1073741825
addr = 0x4010f000
read fault test: start=135059091263 stop=135383514415, elapsed=324423152
write fault test: start=135383569394 stop=135664481836, elapsed=280912442

So, let's see what can be done to speed up the clean to dirty fault
path...  (more later)

		-ben

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