>
> When loading a zero page, check whether it will be loaded to
> persistent memory If yes, load it by libpmem function
> pmem_memset_nodrain(). Combined with a call to pmem_drain() at the
> end of RAM loading, we can guarantee all those zero pages are
> persistently loaded.
>
> Depending on the host HW/SW configurations, pmem_drain() can be
> "sfence". Therefore, we do not call pmem_drain() after each
> pmem_memset_nodrain(), or use pmem_memset_persist() (equally
> pmem_memset_nodrain() + pmem_drain()), in order to avoid unnecessary
> overhead.
Are you saying we don't need 'pmem_drain()'?
I can see its called in patch 5 in ram_load? But
I also see empty definition. Anything I am missing here?
Thanks,
Pankaj
>
> Signed-off-by: Haozhong Zhang <haozhong.zh...@intel.com>
> ---
> include/qemu/pmem.h | 9 +++++++++
> migration/ram.c | 34 +++++++++++++++++++++++++++++-----
> 2 files changed, 38 insertions(+), 5 deletions(-)
>
> diff --git a/include/qemu/pmem.h b/include/qemu/pmem.h
> index 9017596ff0..861d8ecc21 100644
> --- a/include/qemu/pmem.h
> +++ b/include/qemu/pmem.h
> @@ -26,6 +26,15 @@ pmem_memcpy_persist(void *pmemdest, const void *src,
> size_t len)
> return memcpy(pmemdest, src, len);
> }
>
> +static inline void *pmem_memset_nodrain(void *pmemdest, int c, size_t len)
> +{
> + return memset(pmemdest, c, len);
> +}
> +
> +static inline void pmem_drain(void)
> +{
> +}
> +
> #endif /* CONFIG_LIBPMEM */
>
> #endif /* !QEMU_PMEM_H */
> diff --git a/migration/ram.c b/migration/ram.c
> index cb1950f3eb..5a0e503818 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -49,6 +49,7 @@
> #include "qemu/rcu_queue.h"
> #include "migration/colo.h"
> #include "migration/block.h"
> +#include "qemu/pmem.h"
>
> /***********************************************************/
> /* ram save/restore */
> @@ -2467,6 +2468,20 @@ static inline void
> *host_from_ram_block_offset(RAMBlock *block,
> return block->host + offset;
> }
>
> +static void ram_handle_compressed_common(void *host, uint8_t ch, uint64_t
> size,
> + bool is_pmem)
> +{
> + if (!ch && is_zero_range(host, size)) {
> + return;
> + }
> +
> + if (!is_pmem) {
> + memset(host, ch, size);
> + } else {
> + pmem_memset_nodrain(host, ch, size);
> + }
> +}
> +
> /**
> * ram_handle_compressed: handle the zero page case
> *
> @@ -2479,9 +2494,7 @@ static inline void *host_from_ram_block_offset(RAMBlock
> *block,
> */
> void ram_handle_compressed(void *host, uint8_t ch, uint64_t size)
> {
> - if (ch != 0 || !is_zero_range(host, size)) {
> - memset(host, ch, size);
> - }
> + return ram_handle_compressed_common(host, ch, size, false);
> }
>
> static void *do_data_decompress(void *opaque)
> @@ -2823,6 +2836,7 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> bool postcopy_running = postcopy_is_running();
> /* ADVISE is earlier, it shows the source has the postcopy capability on
> */
> bool postcopy_advised = postcopy_is_advised();
> + bool need_pmem_drain = false;
>
> seq_iter++;
>
> @@ -2848,6 +2862,8 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> ram_addr_t addr, total_ram_bytes;
> void *host = NULL;
> uint8_t ch;
> + RAMBlock *block = NULL;
> + bool is_pmem = false;
>
> addr = qemu_get_be64(f);
> flags = addr & ~TARGET_PAGE_MASK;
> @@ -2864,7 +2880,7 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
>
> if (flags & (RAM_SAVE_FLAG_ZERO | RAM_SAVE_FLAG_PAGE |
> RAM_SAVE_FLAG_COMPRESS_PAGE | RAM_SAVE_FLAG_XBZRLE)) {
> - RAMBlock *block = ram_block_from_stream(f, flags);
> + block = ram_block_from_stream(f, flags);
>
> host = host_from_ram_block_offset(block, addr);
> if (!host) {
> @@ -2874,6 +2890,9 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> }
> ramblock_recv_bitmap_set(block, host);
> trace_ram_load_loop(block->idstr, (uint64_t)addr, flags, host);
> +
> + is_pmem = ramblock_is_pmem(block);
> + need_pmem_drain = need_pmem_drain || is_pmem;
> }
>
> switch (flags & ~RAM_SAVE_FLAG_CONTINUE) {
> @@ -2927,7 +2946,7 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
>
> case RAM_SAVE_FLAG_ZERO:
> ch = qemu_get_byte(f);
> - ram_handle_compressed(host, ch, TARGET_PAGE_SIZE);
> + ram_handle_compressed_common(host, ch, TARGET_PAGE_SIZE,
> is_pmem);
> break;
>
> case RAM_SAVE_FLAG_PAGE:
> @@ -2970,6 +2989,11 @@ static int ram_load(QEMUFile *f, void *opaque, int
> version_id)
> }
>
> wait_for_decompress_done();
> +
> + if (need_pmem_drain) {
> + pmem_drain();
> + }
> +
> rcu_read_unlock();
> trace_ram_load_complete(ret, seq_iter);
> return ret;
> --
> 2.14.1
>
>
>
