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Message-ID: <20120816210206.GA17966@phenom.dumpdata.com>
Date: Thu, 16 Aug 2012 17:02:06 -0400
From: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To: linux-kernel@...r.kernel.org, xen-devel@...ts.xensource.com
Subject: Re: [Xen-devel] [PATCH 1/2] xen/p2m: Fix for 32-bit builds the
"Reserve 8MB of _brk space for P2M"
On Thu, Aug 16, 2012 at 01:32:15PM -0400, Konrad Rzeszutek Wilk wrote:
> On Thu, Aug 16, 2012 at 11:50:13AM -0400, Konrad Rzeszutek Wilk wrote:
> > The git commit 5bc6f9888db5739abfa0cae279b4b442e4db8049
> > xen/p2m: Reserve 8MB of _brk space for P2M leafs when populating back.
> >
> > extended the _brk space to fit 1048576 PFNs. The math is that each
> > P2M leaf can cover PAGE_SIZE/sizeof(unsigned long) PFNs. In 64-bit
> > that means 512 PFNs, on 32-bit that is 1024. If on 64-bit machines
> > we want to cover 4GB of PFNs, that means having enough for space
> > to fit 1048576 unsigned longs.
>
> Scratch that patch. This is better, but even with that I am still
> hitting some weird 32-bit cases.
So I thought about this some more and came up with this patch. Its
RFC and going to run it through some overnight tests to see how they fare.
commit da858a92dbeb52fb3246e3d0f1dd57989b5b1734
Author: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Date: Fri Jul 27 16:05:47 2012 -0400
xen/p2m: Reuse existing P2M leafs if they are filled with 1:1 PFNs or INVALID.
If P2M leaf is completly packed with INVALID_P2M_ENTRY or with
1:1 PFNs (so IDENTITY_FRAME type PFNs), we can swap the P2M leaf
with either a p2m_missing or p2m_identity respectively. The old
page (which was created via extend_brk or was grafted on from the
mfn_list) can be re-used for setting new PFNs.
This also means we can remove git commit:
5bc6f9888db5739abfa0cae279b4b442e4db8049
xen/p2m: Reserve 8MB of _brk space for P2M leafs when populating back
which tried to fix this.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index 29244d0..b6b7c10 100644
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -194,11 +194,6 @@ RESERVE_BRK(p2m_mid_mfn, PAGE_SIZE * (MAX_DOMAIN_PAGES / (P2M_PER_PAGE * P2M_MID
* boundary violation will require three middle nodes. */
RESERVE_BRK(p2m_mid_identity, PAGE_SIZE * 2 * 3);
-/* When we populate back during bootup, the amount of pages can vary. The
- * max we have is seen is 395979, but that does not mean it can't be more.
- * Some machines can have 3GB I/O holes so lets reserve for that. */
-RESERVE_BRK(p2m_populated, 786432 * sizeof(unsigned long));
-
static inline unsigned p2m_top_index(unsigned long pfn)
{
BUG_ON(pfn >= MAX_P2M_PFN);
@@ -575,12 +570,99 @@ static bool __init early_alloc_p2m(unsigned long pfn)
}
return true;
}
+
+/*
+ * Skim over the P2M tree looking at pages that are either filled with
+ * INVALID_P2M_ENTRY or with 1:1 PFNs. If found, re-use that page and
+ * replace the P2M leaf with a p2m_missing or p2m_identity.
+ * Stick the old page in the new P2M tree location.
+ */
+bool __init early_can_reuse_p2m_middle(unsigned long set_pfn, unsigned long set_mfn)
+{
+ unsigned topidx;
+ unsigned mididx;
+ unsigned ident_pfns;
+ unsigned inv_pfns;
+ unsigned long *p2m;
+ unsigned long *mid_mfn_p;
+ unsigned idx;
+ unsigned long pfn;
+
+ /* We only look when this entails a P2M middle layer */
+ if (p2m_index(set_pfn))
+ return false;
+
+ for (pfn = 0; pfn <= MAX_DOMAIN_PAGES; pfn += P2M_PER_PAGE) {
+ topidx = p2m_top_index(pfn);
+
+ if (!p2m_top[topidx])
+ continue;
+
+ if (p2m_top[topidx] == p2m_mid_missing)
+ continue;
+
+ mididx = p2m_mid_index(pfn);
+ p2m = p2m_top[topidx][mididx];
+ if (!p2m)
+ continue;
+
+ if ((p2m == p2m_missing) || (p2m == p2m_identity))
+ continue;
+
+ if ((unsigned long)p2m == INVALID_P2M_ENTRY)
+ continue;
+
+ ident_pfns = 0;
+ inv_pfns = 0;
+ for (idx = 0; idx < P2M_PER_PAGE; idx++) {
+ /* IDENTITY_PFNs are 1:1 */
+ if (p2m[idx] == IDENTITY_FRAME(pfn + idx))
+ ident_pfns++;
+ else if (p2m[idx] == INVALID_P2M_ENTRY)
+ inv_pfns++;
+ else
+ break;
+ }
+ if ((ident_pfns == P2M_PER_PAGE) || (inv_pfns == P2M_PER_PAGE))
+ goto found;
+ }
+ return false;
+found:
+ /* Found one, replace old with p2m_identity or p2m_missing */
+ p2m_top[topidx][mididx] = (ident_pfns ? p2m_identity : p2m_missing);
+ /* And the other for save/restore.. */
+ mid_mfn_p = p2m_top_mfn_p[topidx];
+ /* NOTE: Even if it is a p2m_identity it should still be point to
+ * a page filled with INVALID_P2M_ENTRY entries. */
+ mid_mfn_p[mididx] = virt_to_mfn(p2m_missing);
+
+ /* Reset where we want to stick the old page in. */
+ topidx = p2m_top_index(set_pfn);
+ mididx = p2m_mid_index(set_pfn);
+
+ /* This shouldn't happen */
+ if (WARN_ON(p2m_top[topidx] == p2m_mid_missing))
+ early_alloc_p2m(set_pfn);
+
+ if (WARN_ON(p2m_top[topidx][mididx] != p2m_missing))
+ return false;
+
+ p2m_init(p2m);
+ p2m_top[topidx][mididx] = p2m;
+ mid_mfn_p = p2m_top_mfn_p[topidx];
+ mid_mfn_p[mididx] = virt_to_mfn(p2m);
+
+ return true;
+}
bool __init early_set_phys_to_machine(unsigned long pfn, unsigned long mfn)
{
if (unlikely(!__set_phys_to_machine(pfn, mfn))) {
if (!early_alloc_p2m(pfn))
return false;
+ if (early_can_reuse_p2m_middle(pfn, mfn))
+ return __set_phys_to_machine(pfn, mfn);
+
if (!early_alloc_p2m_middle(pfn, false /* boundary crossover OK!*/))
return false;
--
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