On Fri, Oct 03, 2014 at 06:47:35PM +0100, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" <dgilb...@redhat.com> > > The PMI holds the state of each page on the incoming side, > so that we can tell if the page is missing, already received > or there is a request outstanding for it. > > Signed-off-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>
Though there are a couple of minor comments below:
> ---
> include/migration/migration.h | 19 ++++
> include/migration/postcopy-ram.h | 12 +++
> include/qemu/typedefs.h | 1 +
> postcopy-ram.c | 220
> +++++++++++++++++++++++++++++++++++++++
> 4 files changed, 252 insertions(+)
>
> diff --git a/include/migration/migration.h b/include/migration/migration.h
> index 2ff9d35..1405a15 100644
> --- a/include/migration/migration.h
> +++ b/include/migration/migration.h
> @@ -57,6 +57,24 @@ struct MigrationRetPathState {
>
> typedef struct MigrationState MigrationState;
>
> +/* Postcopy page-map-incoming - data about each page on the inbound side */
> +
> +typedef enum {
> + POSTCOPY_PMI_MISSING, /* page hasn't yet been received */
> + POSTCOPY_PMI_REQUESTED, /* Kernel asked for a page, but we've not got it
> */
> + POSTCOPY_PMI_RECEIVED /* We've got the page */
> +} PostcopyPMIState;
> +
> +struct PostcopyPMI {
> + QemuMutex mutex;
> + unsigned long *received_map; /* Pages that we have received */
> + unsigned long *requested_map; /* Pages that we're sending a request for
> */
> + unsigned long host_mask; /* A mask with enough bits set to cover one
> + host page in the PMI */
> + unsigned long host_bits; /* The number of bits in the map
> representing
> + one host page */
> +};
> +
> /* State for the incoming migration */
> struct MigrationIncomingState {
> QEMUFile *file;
> @@ -71,6 +89,7 @@ struct MigrationIncomingState {
>
> QEMUFile *return_path;
> QemuMutex rp_mutex; /* We send replies from multiple threads */
> + PostcopyPMI postcopy_pmi;
> };
>
> MigrationIncomingState *migration_incoming_get_current(void);
> diff --git a/include/migration/postcopy-ram.h
> b/include/migration/postcopy-ram.h
> index dcd1afa..addb88a 100644
> --- a/include/migration/postcopy-ram.h
> +++ b/include/migration/postcopy-ram.h
> @@ -13,7 +13,19 @@
> #ifndef QEMU_POSTCOPY_RAM_H
> #define QEMU_POSTCOPY_RAM_H
>
> +#include "migration/migration.h"
> +
> /* Return 0 if the host supports everything we need to do postcopy-ram */
> int postcopy_ram_hosttest(void);
>
> +/*
> + * In 'advise' mode record that a page has been received.
> + */
> +void postcopy_hook_early_receive(MigrationIncomingState *mis,
> + size_t bitmap_index);
> +
> +void postcopy_pmi_destroy(MigrationIncomingState *mis);
> +void postcopy_pmi_discard_range(MigrationIncomingState *mis,
> + size_t start, size_t npages);
> +void postcopy_pmi_dump(MigrationIncomingState *mis);
> #endif
> diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
> index 8539de6..61b330c 100644
> --- a/include/qemu/typedefs.h
> +++ b/include/qemu/typedefs.h
> @@ -77,6 +77,7 @@ typedef struct QEMUSGList QEMUSGList;
> typedef struct SHPCDevice SHPCDevice;
> typedef struct FWCfgState FWCfgState;
> typedef struct PcGuestInfo PcGuestInfo;
> +typedef struct PostcopyPMI PostcopyPMI;
> typedef struct Range Range;
> typedef struct AdapterInfo AdapterInfo;
>
> diff --git a/postcopy-ram.c b/postcopy-ram.c
> index bba5c71..210585c 100644
> --- a/postcopy-ram.c
> +++ b/postcopy-ram.c
> @@ -23,6 +23,9 @@
> #include "qemu-common.h"
> #include "migration/migration.h"
> #include "migration/postcopy-ram.h"
> +#include "sysemu/sysemu.h"
> +#include "qemu/bitmap.h"
> +#include "qemu/error-report.h"
>
> //#define DEBUG_POSTCOPY
>
> @@ -82,6 +85,216 @@
> #if defined(__linux__) && defined(MADV_USERFAULT) && \
> defined(__NR_remap_anon_pages)
>
> +/* ---------------------------------------------------------------------- */
> +/* Postcopy pagemap-inbound (pmi) - data structures that record the */
> +/* state of each page used by the inbound postcopy */
> +/* It's a pair of bitmaps (of the same structure as the migration bitmaps)*/
> +/* holding one bit per target-page, although all operations work on host */
> +/* pages. */
> +__attribute__ (( unused )) /* Until later in patch series */
> +static void postcopy_pmi_init(MigrationIncomingState *mis, size_t ram_pages)
> +{
> + unsigned int tpb = qemu_target_page_bits();
> + unsigned long host_bits;
> +
> + qemu_mutex_init(&mis->postcopy_pmi.mutex);
> + mis->postcopy_pmi.received_map = bitmap_new(ram_pages);
> + mis->postcopy_pmi.requested_map = bitmap_new(ram_pages);
> + bitmap_clear(mis->postcopy_pmi.received_map, 0, ram_pages);
> + bitmap_clear(mis->postcopy_pmi.requested_map, 0, ram_pages);
> + /*
> + * Each bit in the map represents one 'target page' which is no bigger
> + * than a host page but can be smaller. It's useful to have some
> + * convenience masks for later
So, there's no inherent reason a target page couldn't be bigger than a
host page. It's fair enough not to handle that case for now, but
something somewhere should probably verify that it's no the case.
> + */
> +
> + /*
> + * The number of bits one host page takes up in the bitmap
> + * e.g. on a 64k host page, 4k Target page, host_bits=64/4=16
> + */
> + host_bits = sysconf(_SC_PAGESIZE) / (1ul << tpb);
> + /* Should be a power of 2 */
> + assert(host_bits && !(host_bits & (host_bits - 1)));
> + /*
> + * If the host_bits isn't a division of the number of bits in long
> + * then the code gets a lot more complex; disallow for now
> + * (I'm not aware of a system where it's true anyway)
> + */
> + assert(((sizeof(long) * 8) % host_bits) == 0);
> +
> + mis->postcopy_pmi.host_bits = host_bits;
> + /* A mask, starting at bit 0, containing host_bits continuous set bits */
> + mis->postcopy_pmi.host_mask = (1ul << host_bits) - 1;
> +
> + assert((ram_pages % host_bits) == 0);
> +}
> +
> +void postcopy_pmi_destroy(MigrationIncomingState *mis)
> +{
> + if (mis->postcopy_pmi.received_map) {
> + g_free(mis->postcopy_pmi.received_map);
g_free() is safe to call on NULL anyway, isn't it?
> + mis->postcopy_pmi.received_map = NULL;
> + }
> + if (mis->postcopy_pmi.requested_map) {
> + g_free(mis->postcopy_pmi.requested_map);
> + mis->postcopy_pmi.requested_map = NULL;
> + }
> + qemu_mutex_destroy(&mis->postcopy_pmi.mutex);
> +}
> +
> +/*
> + * Mark a set of pages in the PMI as being clear; this is used by the discard
> + * at the start of postcopy, and before the postcopy stream starts.
> + */
> +void postcopy_pmi_discard_range(MigrationIncomingState *mis,
> + size_t start, size_t npages)
> +{
> + bitmap_clear(mis->postcopy_pmi.received_map, start, npages);
> +}
> +
> +/*
> + * Test a host-page worth of bits in the map starting at bitmap_index
> + * The bits should all be consistent
> + */
> +static bool test_hpbits(MigrationIncomingState *mis,
> + size_t bitmap_index, unsigned long *map)
> +{
> + long masked;
> +
> + assert((bitmap_index & (mis->postcopy_pmi.host_bits-1)) == 0);
> +
> + masked = (map[BIT_WORD(bitmap_index)] >>
> + (bitmap_index % BITS_PER_LONG)) &
> + mis->postcopy_pmi.host_mask;
> +
> + assert((masked == 0) || (masked == mis->postcopy_pmi.host_mask));
> + return !!masked;
> +}
> +
> +/*
> + * Set host-page worth of bits in the map starting at bitmap_index
> + */
> +static void set_hpbits(MigrationIncomingState *mis,
> + size_t bitmap_index, unsigned long *map)
> +{
> + assert((bitmap_index & (mis->postcopy_pmi.host_bits-1)) == 0);
> +
> + map[BIT_WORD(bitmap_index)] |= mis->postcopy_pmi.host_mask <<
> + (bitmap_index % BITS_PER_LONG);
> +}
> +
> +/*
> + * Clear host-page worth of bits in the map starting at bitmap_index
> + */
> +static void clear_hpbits(MigrationIncomingState *mis,
> + size_t bitmap_index, unsigned long *map)
> +{
> + assert((bitmap_index & (mis->postcopy_pmi.host_bits-1)) == 0);
> +
> + map[BIT_WORD(bitmap_index)] &= ~(mis->postcopy_pmi.host_mask <<
> + (bitmap_index % BITS_PER_LONG));
> +}
> +
> +/*
> + * Retrieve the state of the given page
> + * Note: This version for use by callers already holding the lock
> + */
> +static PostcopyPMIState postcopy_pmi_get_state_nolock(
> + MigrationIncomingState *mis,
> + size_t bitmap_index)
> +{
> + bool received, requested;
> +
> + received = test_hpbits(mis, bitmap_index,
> mis->postcopy_pmi.received_map);
> + requested = test_hpbits(mis, bitmap_index,
> mis->postcopy_pmi.requested_map);
> +
> + if (received) {
> + assert(!requested);
Clearing the requested bit when you set the received bit seems a bit
pointless. (requested && received) isn't meaningfully different from
(!requested && received) but there seems no reason to go to extra
trouble to avoid that state, and having the record might be
interesting for gathering statistics.
> + return POSTCOPY_PMI_RECEIVED;
> + } else {
> + return requested ? POSTCOPY_PMI_REQUESTED : POSTCOPY_PMI_MISSING;
> + }
> +}
> +
> +/* Retrieve the state of the given page */
> +__attribute__ (( unused )) /* Until later in patch series */
> +static PostcopyPMIState postcopy_pmi_get_state(MigrationIncomingState *mis,
> + size_t bitmap_index)
> +{
> + PostcopyPMIState ret;
> + qemu_mutex_lock(&mis->postcopy_pmi.mutex);
> + ret = postcopy_pmi_get_state_nolock(mis, bitmap_index);
> + qemu_mutex_unlock(&mis->postcopy_pmi.mutex);
> +
> + return ret;
> +}
> +
> +/*
> + * Set the page state to the given state if the previous state was as
> expected
> + * Return the actual previous state.
> + */
> +__attribute__ (( unused )) /* Until later in patch series */
> +static PostcopyPMIState postcopy_pmi_change_state(MigrationIncomingState
> *mis,
> + size_t bitmap_index,
> + PostcopyPMIState expected_state,
> + PostcopyPMIState new_state)
> +{
> + PostcopyPMIState old_state;
> +
> + qemu_mutex_lock(&mis->postcopy_pmi.mutex);
> + old_state = postcopy_pmi_get_state_nolock(mis, bitmap_index);
> +
> + if (old_state == expected_state) {
> + switch (new_state) {
> + case POSTCOPY_PMI_MISSING:
> + assert(0); /* This shouldn't actually happen - use discard_range */
> + break;
> +
> + case POSTCOPY_PMI_REQUESTED:
> + assert(old_state == POSTCOPY_PMI_MISSING);
> + set_hpbits(mis, bitmap_index, mis->postcopy_pmi.requested_map);
> + break;
> +
> + case POSTCOPY_PMI_RECEIVED:
> + assert(old_state == POSTCOPY_PMI_MISSING ||
> + old_state == POSTCOPY_PMI_REQUESTED);
> + set_hpbits(mis, bitmap_index, mis->postcopy_pmi.received_map);
> + clear_hpbits(mis, bitmap_index, mis->postcopy_pmi.requested_map);
> + break;
> + }
> + }
> +
> + qemu_mutex_unlock(&mis->postcopy_pmi.mutex);
> + return old_state;
> +}
> +
> +/*
> + * Useful when debugging postcopy, although if it failed early the
> + * received map can be quite sparse and thus big when dumped.
> + */
> +void postcopy_pmi_dump(MigrationIncomingState *mis)
> +{
> + fprintf(stderr, "postcopy_pmi_dump: requested\n");
> + ram_debug_dump_bitmap(mis->postcopy_pmi.requested_map, false);
> + fprintf(stderr, "postcopy_pmi_dump: received\n");
> + ram_debug_dump_bitmap(mis->postcopy_pmi.received_map, true);
> + fprintf(stderr, "postcopy_pmi_dump: end\n");
> +}
> +
> +/* Called by ram_load prior to mapping the page */
> +void postcopy_hook_early_receive(MigrationIncomingState *mis,
> + size_t bitmap_index)
> +{
> + if (mis->postcopy_ram_state == POSTCOPY_RAM_INCOMING_ADVISE) {
A silent no-op if you're not in the expected migration phase doesn't
seem right. Should this be an assert() instead?
> + /*
> + * If we're in precopy-advise mode we need to track received pages
> even
> + * though we don't need to place pages atomically yet.
> + * In advise mode there's only a single thread, so don't need locks
> + */
> + set_bit(bitmap_index, mis->postcopy_pmi.received_map);
> + }
> +}
> +
> int postcopy_ram_hosttest(void)
> {
> /* TODO: Needs guarding with CONFIG_ once we have libc's that have the
> defs
> @@ -156,5 +369,12 @@ int postcopy_ram_hosttest(void)
> return -1;
> }
>
> +/* Called by ram_load prior to mapping the page */
> +void postcopy_hook_early_receive(MigrationIncomingState *mis,
> + size_t bitmap_index)
> +{
> + /* We don't support postcopy so don't care */
> +}
> +
> #endif
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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