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Message-ID: <502E2784.8060806@citrix.com>
Date: Fri, 17 Aug 2012 12:14:12 +0100
From: David Vrabel <david.vrabel@...rix.com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
CC: <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 16/08/12 22:02, Konrad Rzeszutek Wilk wrote:
>
> 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.
Does this actually find any p2m pages to reclaim?
xen_set_identity_and_release() is careful to set the largest possible
range as 1:1 and the comments at the top of p2m.c suggest the mid
entries will be made to point to p2m_identity already.
David
> 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;
>
>
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@...ts.xen.org
> http://lists.xen.org/xen-devel
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