On Fri, Feb 16, 2018 at 01:15:57PM +0000, Dr. David Alan Gilbert (git) wrote: > From: "Dr. David Alan Gilbert" <[email protected]> > > The choice of call to discard a block is getting more complicated > for other cases. We use fallocate PUNCH_HOLE in any file cases; > it works for both hugepage and for tmpfs. > We use the DONTNEED for non-hugepage cases either where they're > anonymous or where they're private. > > Care should be taken when trying other backing files. > > Signed-off-by: Dr. David Alan Gilbert <[email protected]> > --- > exec.c | 60 > ++++++++++++++++++++++++++++++++++++++++++++++-------------- > trace-events | 3 ++- > 2 files changed, 48 insertions(+), 15 deletions(-) > > diff --git a/exec.c b/exec.c > index e8d7b335b6..b1bb477776 100644 > --- a/exec.c > +++ b/exec.c > @@ -3702,6 +3702,7 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t > start, size_t length) > } > > if ((start + length) <= rb->used_length) { > + bool need_madvise, need_fallocate; > uint8_t *host_endaddr = host_startaddr + length; > if ((uintptr_t)host_endaddr & (rb->page_size - 1)) { > error_report("ram_block_discard_range: Unaligned end address: > %p", > @@ -3711,29 +3712,60 @@ int ram_block_discard_range(RAMBlock *rb, uint64_t > start, size_t length) > > errno = ENOTSUP; /* If we are missing MADVISE etc */ > > - if (rb->page_size == qemu_host_page_size) { > -#if defined(CONFIG_MADVISE) > - /* Note: We need the madvise MADV_DONTNEED behaviour of > definitely > - * freeing the page. > - */ > - ret = madvise(host_startaddr, length, MADV_DONTNEED); > -#endif > - } else { > - /* Huge page case - unfortunately it can't do DONTNEED, but > - * it can do the equivalent by FALLOC_FL_PUNCH_HOLE in the > - * huge page file. > + /* The logic here is messy; > + * madvise DONTNEED fails for hugepages > + * fallocate works on hugepages and shmem > + */ > + need_madvise = (rb->page_size == qemu_host_page_size); > + need_fallocate = rb->fd != -1; > + if (need_fallocate) { > + /* For a file, this causes the area of the file to be zero'd > + * if read, and for hugetlbfs also causes it to be unmapped > + * so a userfault will trigger. > */ > #ifdef CONFIG_FALLOCATE_PUNCH_HOLE > ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE | > FALLOC_FL_KEEP_SIZE, > start, length); > + if (ret) { > + ret = -errno; > + error_report("ram_block_discard_range: Failed to fallocate " > + "%s:%" PRIx64 " +%zx (%d)", > + rb->idstr, start, length, ret); > + goto err; > + } > +#else > + ret = -ENOSYS; > + error_report("ram_block_discard_range: fallocate not > available/file" > + "%s:%" PRIx64 " +%zx (%d)", > + rb->idstr, start, length, ret); > + goto err; > #endif > } > - if (ret) { > - ret = -errno; > - error_report("ram_block_discard_range: Failed to discard range " > + if (need_madvise) { > + /* For normal RAM this causes it to be unmapped, > + * for shared memory it causes the local mapping to disappear > + * and to fall back on the file contents (which we just > + * fallocate'd away). > + */ > +#if defined(CONFIG_MADVISE) > + ret = madvise(host_startaddr, length, MADV_DONTNEED); > + if (ret) { > + ret = -errno; > + error_report("ram_block_discard_range: Failed to discard > range " > + "%s:%" PRIx64 " +%zx (%d)", > + rb->idstr, start, length, ret); > + goto err; > + } > +#else > + ret = -ENOSYS; > + error_report("ram_block_discard_range: MADVISE not available" > "%s:%" PRIx64 " +%zx (%d)", > rb->idstr, start, length, ret); > + goto err; > +#endif > } > + trace_ram_block_discard_range(rb->idstr, host_startaddr, > + need_madvise, need_fallocate, ret);
Nit: worth to log the length too if it's named as "range"? Either with/without: Reviewed-by: Peter Xu <[email protected]> -- Peter Xu
