Re: Linux 2.4.10-pre11

Andrea Arcangeli
2001-09-18T03:37:17Z

On Mon, Sep 17, 2001 at 10:08:22PM -0300, Marcelo Tosatti wrote:
>
>
> On Mon, 17 Sep 2001, Marcelo Tosatti wrote:
>
> >
> >
> > On Mon, 17 Sep 2001, Linus Torvalds wrote:
> >
> > >
> > > Ok, the big thing here is continued merging, this time with Andrea.
> > >
> > > I still don't like some of the VM changes, but integrating Andrea's VM
> > > changes results in (a) better performance and (b) much cleaner inactive
> > > page handling in particular. Besides, for the 2.4.x tree, the big priority
> > > is stability, we can re-address my other concerns during 2.5.x.
> >
> > Andrea,
> >
> > Could you please make a resume of your VM changes ?
> >
> > Its hard to keep up with VM changes this way.
>
> Andrea,
>
> I've just read a bit of your new VM code and I have a few comments.
>
> You completly removed the "inactive freeable pages" logic: There is no

yes, it wasn't relly useful to keep this list lazily, you either keep it
enforced with locking overhead or such information isn't valuable.

> more distiction between "freeable inactive" and "free" pages. All VM work
> is based on "freepages.high" watermark. I don't like that: it seems to

hardly on freepages.high:

diff -urN vm-ref/mm/swap.c vm/mm/swap.c
--- vm-ref/mm/swap.c Tue Sep 18 00:18:17 2001
+++ vm/mm/swap.c Tue Sep 18 00:18:35 2001
@@ -24,50 +24,13 @@
#include <asm/uaccess.h> /* for copy_to/from_user */
#include <asm/pgtable.h>

-/*
- * We identify three levels of free memory. We never let free mem
- * fall below the freepages.min except for atomic allocations. We
- * start background swapping if we fall below freepages.high free
- * pages, and we begin intensive swapping below freepages.low.
- *
- * Actual initialization is done in mm/page_alloc.c
- */
-freepages_t freepages = {
- 0, /* freepages.min */
- 0, /* freepages.low */
- 0 /* freepages.high */
-};
-

> make page freeing more aggressive over time.

I don't see your point with "page freeing more aggressive over time".

> Also, if we have several try_to_free_pages() callers, for different
> classzones, I'm right saying that a caller with a "smaller" classzone can
> "hide" pages in its "active_local_lru" and/or "inactive_local_lru" (during
> shrink_cache) from other processes trying to free pages from those higher
> zones ?

I'm deeply impressed, you seem to have understood the rewrite greatly
well, congrats, this "hiding" was infact my main concern I had on the
memclass check during shrink_cache, but I don't think this will ever
give us troubles. In such there are suprious swapouts with HIGHMEM
we'll just need to waste some cpu by lefting those pages visible with a
few changes in shrink_cache, but again I'm almost sure there won't be
problems, we do multiple scans before failing so those pages will return
visible before the other task has a chance to fail the allocation.

Andrea