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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] libxc: try to find last used pfn when migrating
On 27/11/15 14:50, Juergen Gross wrote:
> For migration the last used pfn of a guest is needed to size the
> logdirty bitmap and as an upper bound of the page loop. Unfortunately
> there are pv-kernels advertising a much higher maximum pfn as they
> are really using in order to support memory hotplug. This will lead
> to allocation of much more memory in Xen tools during migration as
> really needed.
>
> Try to find the last used guest pfn of a pv-domu by scanning the p2m
> tree from the last entry towards it's start and search for an entry
> not being invalid.
>
> Normally the mid pages of the p2m tree containing all invalid entries
> are being reused, so we can just scan the top page for identical
> entries and skip them but the first one.
>
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> ---
> tools/libxc/xc_sr_save.c | 8 ++++----
> tools/libxc/xc_sr_save_x86_pv.c | 34 +++++++++++++++++++++++++++++++---
> 2 files changed, 35 insertions(+), 7 deletions(-)
>
> diff --git a/tools/libxc/xc_sr_save.c b/tools/libxc/xc_sr_save.c
> index 0c12e56..22b3f18 100644
> --- a/tools/libxc/xc_sr_save.c
> +++ b/tools/libxc/xc_sr_save.c
> @@ -677,6 +677,10 @@ static int setup(struct xc_sr_context *ctx)
> DECLARE_HYPERCALL_BUFFER_SHADOW(unsigned long, dirty_bitmap,
> &ctx->save.dirty_bitmap_hbuf);
>
> + rc = ctx->save.ops.setup(ctx);
> + if ( rc )
> + goto err;
> +
> dirty_bitmap = xc_hypercall_buffer_alloc_pages(
> xch, dirty_bitmap,
> NRPAGES(bitmap_size(ctx->save.p2m_size)));
> ctx->save.batch_pfns = malloc(MAX_BATCH_SIZE *
> @@ -692,10 +696,6 @@ static int setup(struct xc_sr_context *ctx)
> goto err;
> }
>
> - rc = ctx->save.ops.setup(ctx);
> - if ( rc )
> - goto err;
> -
> rc = 0;
>
> err:
While moving this, the restore side should be consistent (turns out it
already is), and the docs updated. There was an inaccuracy, so I went
ahead and did it.
--8<--
diff --git a/tools/libxc/xc_sr_common.h b/tools/libxc/xc_sr_common.h
index 64f6082..ae77155 100644
--- a/tools/libxc/xc_sr_common.h
+++ b/tools/libxc/xc_sr_common.h
@@ -54,9 +54,11 @@ struct xc_sr_save_ops
void **page);
/**
- * Set up local environment to restore a domain. This is called before
- * any records are written to the stream. (Typically querying running
- * domain state, setting up mappings etc.)
+ * Set up local environment to save a domain. (Typically querying
+ * running domain state, setting up mappings etc.)
+ *
+ * This is called once before any common setup has occurred,
allowing for
+ * guest-specific adjustments to be made to common state.
*/
int (*setup)(struct xc_sr_context *ctx);
@@ -121,8 +123,10 @@ struct xc_sr_restore_ops
int (*localise_page)(struct xc_sr_context *ctx, uint32_t type, void
*page);
/**
- * Set up local environment to restore a domain. This is called before
- * any records are read from the stream.
+ * Set up local environment to restore a domain.
+ *
+ * This is called once before any common setup has occurred,
allowing for
+ * guest-specific adjustments to be made to common state.
*/
int (*setup)(struct xc_sr_context *ctx);
--8<--
Feel free to fold this into your patch, or I can submit it alone as a
cleanup prerequisite for your functional change below.
> diff --git a/tools/libxc/xc_sr_save_x86_pv.c b/tools/libxc/xc_sr_save_x86_pv.c
> index f63f40b..6189fda 100644
> --- a/tools/libxc/xc_sr_save_x86_pv.c
> +++ b/tools/libxc/xc_sr_save_x86_pv.c
> @@ -83,8 +83,8 @@ static int map_p2m(struct xc_sr_context *ctx)
> */
> xc_interface *xch = ctx->xch;
> int rc = -1;
> - unsigned x, fpp, fll_entries, fl_entries;
> - xen_pfn_t fll_mfn;
> + unsigned x, saved_x, fpp, fll_entries, fl_entries;
> + xen_pfn_t fll_mfn, saved_mfn, max_pfn;
>
> xen_pfn_t *local_fll = NULL;
> void *guest_fll = NULL;
> @@ -96,7 +96,6 @@ static int map_p2m(struct xc_sr_context *ctx)
>
> fpp = PAGE_SIZE / ctx->x86_pv.width;
> fll_entries = (ctx->x86_pv.max_pfn / (fpp * fpp)) + 1;
> - fl_entries = (ctx->x86_pv.max_pfn / fpp) + 1;
>
> fll_mfn = GET_FIELD(ctx->x86_pv.shinfo, arch.pfn_to_mfn_frame_list_list,
> ctx->x86_pv.width);
> @@ -131,6 +130,8 @@ static int map_p2m(struct xc_sr_context *ctx)
> }
>
> /* Check for bad mfns in frame list list. */
> + saved_mfn = 0;
> + saved_x = 0;
> for ( x = 0; x < fll_entries; ++x )
> {
> if ( local_fll[x] == 0 || local_fll[x] > ctx->x86_pv.max_mfn )
> @@ -139,8 +140,35 @@ static int map_p2m(struct xc_sr_context *ctx)
> local_fll[x], x, fll_entries);
> goto err;
> }
> + if ( local_fll[x] != saved_mfn )
> + {
> + saved_mfn = local_fll[x];
> + saved_x = x;
> + }
> }
>
> + /*
> + * Check for actual lower max_pfn:
> + * If the trailing entries of the frame list list were all the same we
> can
> + * assume they all reference mid pages all referencing p2m pages with all
> + * invalid entries. Otherwise there would be multiple pfns referencing
> all
> + * the same mfn which can't work across migration, as this sharing would
> be
> + * broken by the migration process.
> + * Adjust max_pfn if possible to avoid allocating much larger areas as
> + * needed for p2m and logdirty map.
> + */
> + max_pfn = (saved_x + 1) * fpp * fpp - 1;
> + if ( max_pfn < ctx->x86_pv.max_pfn )
> + {
> + ctx->x86_pv.max_pfn = max_pfn;
> + ctx->x86_pv.p2m_frames = (ctx->x86_pv.max_pfn + fpp) / fpp;
> + ctx->save.p2m_size = max_pfn + 1;
> + fll_entries = (ctx->x86_pv.max_pfn / (fpp * fpp)) + 1;
> + DPRINTF("lowering max_pfn to %#lx, p2m_frames %d", max_pfn,
> + ctx->x86_pv.p2m_frames);
> + }
> + fl_entries = (ctx->x86_pv.max_pfn / fpp) + 1;
> +
> /* Map the guest mid p2m frames. */
> guest_fl = xc_map_foreign_pages(xch, ctx->domid, PROT_READ,
> local_fll, fll_entries);
For the actual change, Reviewed-by: Andrew Cooper
<andrew.cooper3@xxxxxxxxxx>
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