Re: [uml-devel] mlock discussion is back - was: Re: [uml-user] odd ping problems

[BlaisorBlade <bla...@ya...>]

Alle 01:23, gioved=EC 27 maggio 2004, roland ha scritto:
> for at least two of the uml-pid`s you should see minor and major pagefaul=
ts
> (minflt/majflt) - i would say there is a releationship between those
> pagefaults and the ping delays. (i had turned off swap completely - so my
> host was not able to swap at all!)

That is not very good - if the latency problem comes from UML being swapped=
=20
out, why do you disable swapping? Actually there is some "swapping", in a=20
certain sense, so you could observe the major page faults (major means=20
"requiring I/O", minor means "no IO": this can happen for COW pages, to mar=
k=20
as dirty a clean page).

When swapping is disabled, the pages belonging to a memory mapping, that wa=
s=20
not modified since they were read from the disk, can be swapped out.

I.e. the executable pages, actually, are created by mmap'ing the executable=
;=20
since they are not modified, they can be removed from memory.

Also the data pages which come from the executable can be treated the same=
=20
way, if they are still "clean" (i.e. not modified).

[ I actually checked the code works this way, i.e. if you try to read a glo=
bal=20
var, even if it's mmaped with PROT_WRITE, in the page-tables it is marked a=
s=20
read-only; when you try to write it, it will be marked as read-write and th=
e=20
page will become dirty. ]

=2D-=20
Paolo Giarrusso, aka Blaisorblade
Linux registered user n. 292729