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Re: [Qemu-devel] [PATCH v5 35/45] postcopy_ram.c: place_page and helpers
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v5 35/45] postcopy_ram.c: place_page and helpers |
Date: |
Wed, 25 Mar 2015 17:46:30 +0000 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
* David Gibson (address@hidden) wrote:
> On Wed, Feb 25, 2015 at 04:51:58PM +0000, Dr. David Alan Gilbert (git) wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> >
> > postcopy_place_page (etc) provide a way for postcopy to place a page
> > into guests memory atomically (using the copy ioctl on the ufd).
> >
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> > include/migration/migration.h | 2 +
> > include/migration/postcopy-ram.h | 16 ++++++
> > migration/postcopy-ram.c | 113
> > ++++++++++++++++++++++++++++++++++++++-
> > trace-events | 1 +
> > 4 files changed, 130 insertions(+), 2 deletions(-)
> >
> > diff --git a/include/migration/migration.h b/include/migration/migration.h
> > index b1c7cad..139bb1b 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -94,6 +94,8 @@ struct MigrationIncomingState {
> > QEMUFile *return_path;
> > QemuMutex rp_mutex; /* We send replies from multiple threads */
> > PostcopyPMI postcopy_pmi;
> > + void *postcopy_tmp_page;
> > + long postcopy_place_skipped; /* Check for incorrect place
> > ops */
> > };
> >
> > MigrationIncomingState *migration_incoming_get_current(void);
> > diff --git a/include/migration/postcopy-ram.h
> > b/include/migration/postcopy-ram.h
> > index fbb2a93..3d30280 100644
> > --- a/include/migration/postcopy-ram.h
> > +++ b/include/migration/postcopy-ram.h
> > @@ -80,4 +80,20 @@ void postcopy_discard_send_chunk(MigrationState *ms,
> > PostcopyDiscardState *pds,
> > void postcopy_discard_send_finish(MigrationState *ms,
> > PostcopyDiscardState *pds);
> >
> > +/*
> > + * Place a page (from) at (host) efficiently
> > + * There are restrictions on how 'from' must be mapped, in general best
> > + * to use other postcopy_ routines to allocate.
> > + * returns 0 on success
> > + */
> > +int postcopy_place_page(MigrationIncomingState *mis, void *host, void
> > *from,
> > + long bitmap_offset, bool all_zero);
> > +
> > +/*
> > + * Allocate a page of memory that can be mapped at a later point in time
> > + * using postcopy_place_page
> > + * Returns: Pointer to allocated page
> > + */
> > +void *postcopy_get_tmp_page(MigrationIncomingState *mis);
> > +
> > #endif
> > diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
> > index 33dd332..86fa5a0 100644
> > --- a/migration/postcopy-ram.c
> > +++ b/migration/postcopy-ram.c
> > @@ -197,7 +197,6 @@ static PostcopyPMIState postcopy_pmi_get_state_nolock(
> > }
> >
> > /* 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)
> > {
> > @@ -213,7 +212,6 @@ static PostcopyPMIState
> > postcopy_pmi_get_state(MigrationIncomingState *mis,
> > * 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,
> > @@ -477,6 +475,7 @@ static int cleanup_area(const char *block_name, void
> > *host_addr,
> > int postcopy_ram_incoming_init(MigrationIncomingState *mis, size_t
> > ram_pages)
> > {
> > postcopy_pmi_init(mis, ram_pages);
> > + mis->postcopy_place_skipped = -1;
> >
> > if (qemu_ram_foreach_block(init_area, mis)) {
> > return -1;
> > @@ -495,6 +494,10 @@ int
> > postcopy_ram_incoming_cleanup(MigrationIncomingState *mis)
> > return -1;
> > }
> >
> > + if (mis->postcopy_tmp_page) {
> > + munmap(mis->postcopy_tmp_page, getpagesize());
> > + mis->postcopy_tmp_page = NULL;
> > + }
> > return 0;
> > }
> >
> > @@ -561,6 +564,100 @@ int postcopy_ram_enable_notify(MigrationIncomingState
> > *mis)
> > return 0;
> > }
> >
> > +/*
> > + * Place a host page (from) at (host) tomically
>
> s/tomically/atomically/
Done.
> > + * There are restrictions on how 'from' must be mapped, in general best
> > + * to use other postcopy_ routines to allocate.
> > + * all_zero: Hint that the page being placed is 0 throughout
> > + * returns 0 on success
> > + * bitmap_offset: Index into the migration bitmaps
> > + *
> > + * State changes:
> > + * none -> received
> > + * requested -> received (ack)
> > + *
> > + * Note the UF thread is also updating the state, and maybe none->requested
> > + * at the same time.
>
> Hrm.. these facts do tend me towards thinking that separate and
> explicit requested and received bits will be clearer than treating it
> as an enum state variable
This is all about to get simpler; Andrea realised he can make a small
change to the kernel interface semantics that means that I no longer have
to keep the destination side bitmaps. That saves all this messing about
updating page states at all.
> > + */
> > +int postcopy_place_page(MigrationIncomingState *mis, void *host, void
> > *from,
> > + long bitmap_offset, bool all_zero)
> > +{
> > + PostcopyPMIState old_state, tmp_state, new_state;
> > +
> > + if (!all_zero) {
> > + struct uffdio_copy copy_struct;
> > +
> > + copy_struct.dst = (uint64_t)(uintptr_t)host;
> > + copy_struct.src = (uint64_t)(uintptr_t)from;
> > + copy_struct.len = getpagesize();
> > + copy_struct.mode = 0;
> > +
> > + /* copy also acks to the kernel waking the stalled thread up
> > + * TODO: We can inhibit that ack and only do it if it was requested
> > + * which would be slightly cheaper, but we'd have to be careful
> > + * of the order of updating our page state.
> > + */
> > + if (ioctl(mis->userfault_fd, UFFDIO_COPY, ©_struct)) {
> > + int e = errno;
> > + error_report("%s: %s copy host: %p from: %p pmi=%d",
> > + __func__, strerror(e), host, from,
> > + postcopy_pmi_get_state(mis, bitmap_offset));
> > +
> > + return -e;
> > + }
> > + } else {
> > + struct uffdio_zeropage zero_struct;
> > +
> > + zero_struct.range.start = (uint64_t)(uintptr_t)host;
> > + zero_struct.range.len = getpagesize();
> > + zero_struct.mode = 0;
> > +
> > + if (ioctl(mis->userfault_fd, UFFDIO_ZEROPAGE, &zero_struct)) {
> > + int e = errno;
> > + error_report("%s: %s zero host: %p from: %p pmi=%d",
> > + __func__, strerror(e), host, from,
> > + postcopy_pmi_get_state(mis, bitmap_offset));
> > +
> > + return -e;
> > + }
> > + }
> > +
> > + bitmap_offset &= ~(mis->postcopy_pmi.host_bits-1);
> > + new_state = POSTCOPY_PMI_RECEIVED;
> > + tmp_state = postcopy_pmi_get_state(mis, bitmap_offset);
> > + do {
> > + old_state = tmp_state;
> > + tmp_state = postcopy_pmi_change_state(mis, bitmap_offset,
> > old_state,
> > + new_state);
> > + } while (old_state != tmp_state);
>
> Yeah.. see treating the state as two separate booleans, here you'd
> just need to update received, without caring about whether requested
> has changed.
It's all very dependent on the exact things you need to do with the states;
whenever you get into a situation where you have to do something on a
combination
of the bits you suddenly have to be a lot more careful.
Anyway, as I say, both of those bits are about to disappear.
Dave
>
> > + trace_postcopy_place_page(bitmap_offset, host, all_zero, old_state);
> > +
> > + return 0;
> > +}
> > +
> > +/*
> > + * Returns a target page of memory that can be mapped at a later point in
> > time
> > + * using postcopy_place_page
> > + * The same address is used repeatedly, postcopy_place_page just takes the
> > + * backing page away.
> > + * Returns: Pointer to allocated page
> > + *
> > + */
> > +void *postcopy_get_tmp_page(MigrationIncomingState *mis)
> > +{
> > + if (!mis->postcopy_tmp_page) {
> > + mis->postcopy_tmp_page = mmap(NULL, getpagesize(),
> > + PROT_READ | PROT_WRITE, MAP_PRIVATE |
> > + MAP_ANONYMOUS, -1, 0);
> > + if (!mis->postcopy_tmp_page) {
> > + perror("mapping postcopy tmp page");
> > + return NULL;
> > + }
> > + }
> > +
> > + return mis->postcopy_tmp_page;
> > +}
> > +
> > #else
> > /* No target OS support, stubs just fail */
> > bool postcopy_ram_supported_by_host(void)
> > @@ -608,6 +705,18 @@ int postcopy_ram_enable_notify(MigrationIncomingState
> > *mis)
> > {
> > assert(0);
> > }
> > +
> > +int postcopy_place_page(MigrationIncomingState *mis, void *host, void
> > *from,
> > + long bitmap_offset, bool all_zero)
> > +{
> > + assert(0);
> > +}
> > +
> > +void *postcopy_get_tmp_page(MigrationIncomingState *mis)
> > +{
> > + assert(0);
> > +}
> > +
> > #endif
> >
> > /*
> > ------------------------------------------------------------------------- */
> > diff --git a/trace-events b/trace-events
> > index 781cf5c..16a91d9 100644
> > --- a/trace-events
> > +++ b/trace-events
> > @@ -1497,6 +1497,7 @@
> > rdma_start_outgoing_migration_after_rdma_source_init(void) ""
> > postcopy_discard_send_finish(const char *ramblock, int nwords, int ncmds)
> > "%s mask words sent=%d in %d commands"
> > postcopy_cleanup_area(const char *ramblock, void *host_addr, size_t
> > offset, size_t length) "%s: %p offset=%zx length=%zx"
> > postcopy_init_area(const char *ramblock, void *host_addr, size_t offset,
> > size_t length) "%s: %p offset=%zx length=%zx"
> > +postcopy_place_page(unsigned long offset, void *host_addr, bool all_zero,
> > int old_state) "offset=%lx host=%p all_zero=%d old_state=%d"
> >
> > # kvm-all.c
> > kvm_ioctl(int type, void *arg) "type 0x%x, arg %p"
>
> --
> 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
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK