On Thu, 7 Sep 2000, Tigran Aivazian wrote:
> On Thu, 7 Sep 2000, Linus Torvalds wrote:
>
> >
> >
> > On Thu, 7 Sep 2000, Tigran Aivazian wrote:
> > >
> > > k) all swapout functions in mm/vmscan.c can be optimized by removing 'mm'
> > > argument. This part was reviewed by Rick van Riel and approved.
> >
> > But they then get "mm" themselves anyway.
> >
> > What's the point? With argument passing, on certain architectures it stays
> > in registers. On other architectures it is in memory on the stack, but
> > that's not slower than accessing it from memory off another pointer.
> >
> > Linus
>
> Linus, I am sorry to say this (because I know you are busy) but it would
> appear you didn't look at the patch (that part of it). The patch does the
> right thing, I believe, but my description was too brief.
>
> If you look at those functions you will see that they sometimes access
> 'mm' via argument and sometimes via vm_mm->mm - this is a complete mess so
> my patch tidies it up a bit.
>
> In other words, if that 'mm' is available via vm_mm->mm there is no point
> in passing it on the stack. Or if we pass it on the stack, there is no
> point accessing it via vm_mm->mm. See my point now?
in case, even this is too brief, here is more:
... so, I had a choice between:
a) remove 'mm' argument
or
b) make all access to 'mm' go via this 'mm' argument
and I thought removing the argument, i.e. choice a) was better than b).
And, yes, I do understand how arguments are passed and what gcc can do
about it.
Regards,
Tigran
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