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Re: [Qemu-devel] [PATCH 05/15] postcopy: enhance ram_discard_range for h
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 05/15] postcopy: enhance ram_discard_range for hugepages |
Date: |
Mon, 30 Jan 2017 18:49:57 +0000 |
User-agent: |
Mutt/1.7.1 (2016-10-04) |
* Juan Quintela (address@hidden) wrote:
> "Dr. David Alan Gilbert (git)" <address@hidden> wrote:
> > From: "Dr. David Alan Gilbert" <address@hidden>
> >
> > Unfortunately madvise DONTNEED doesn't work on hugepagetlb
> > so use fallocate(FALLOC_FL_PUNCH_HOLE)
> > qemu_fd_getpagesize only sets the page based off a file
> > if the file is from hugetlbfs.
> >
> > Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> > ---
> > migration/ram.c | 24 ++++++++++++++++++++----
> > 1 file changed, 20 insertions(+), 4 deletions(-)
> >
> > diff --git a/migration/ram.c b/migration/ram.c
> > index fe32836..7afabcd 100644
> > --- a/migration/ram.c
> > +++ b/migration/ram.c
> > @@ -45,6 +45,10 @@
> > #include "qemu/rcu_queue.h"
> > #include "migration/colo.h"
> >
> > +#if defined(CONFIG_FALLOCATE_PUNCH_HOLE)
> > +#include <linux/falloc.h>
> > +#endif
> > +
> > #ifdef DEBUG_MIGRATION_RAM
> > #define DPRINTF(fmt, ...) \
> > do { fprintf(stdout, "migration_ram: " fmt, ## __VA_ARGS__); } while
> > (0)
> > @@ -1866,7 +1870,7 @@ int ram_discard_range(MigrationIncomingState *mis,
> >
> > uint8_t *host_startaddr = rb->host + start;
> >
> > - if ((uintptr_t)host_startaddr & (qemu_host_page_size - 1)) {
> > + if ((uintptr_t)host_startaddr & (rb->page_size - 1)) {
> > error_report("ram_discard_range: Unaligned start address: %p",
> > host_startaddr);
> > goto err;
> > @@ -1874,15 +1878,27 @@ int ram_discard_range(MigrationIncomingState *mis,
> >
> > if ((start + length) <= rb->used_length) {
> > uint8_t *host_endaddr = host_startaddr + length;
> > - if ((uintptr_t)host_endaddr & (qemu_host_page_size - 1)) {
> > + if ((uintptr_t)host_endaddr & (rb->page_size - 1)) {
> > error_report("ram_discard_range: Unaligned end address: %p",
> > host_endaddr);
> > goto err;
> > }
> > - errno = ENOTSUP;
> > + errno = ENOTSUP; /* If we are missing MADVISE etc */
> > +
> > + if (rb->page_size == qemu_host_page_size) {
> > #if defined(CONFIG_MADVISE)
> > - ret = qemu_madvise(host_startaddr, length, QEMU_MADV_DONTNEED);
> > + ret = qemu_madvise(host_startaddr, length, QEMU_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.
> > + */
> > +#ifdef CONFIG_FALLOCATE_PUNCH_HOLE
> > + ret = fallocate(rb->fd, FALLOC_FL_PUNCH_HOLE |
> > FALLOC_FL_KEEP_SIZE,
> > + start, length);
> > +#endif
> > + }
> > if (ret) {
> > error_report("ram_discard_range: Failed to discard range "
> > "%s:%" PRIx64 " +%zx (%d)",
>
> Can we move this to qemu-posix or similar?
> qemu_punch_hole() or similar and just put all the magic there?
I'm trying but it's tricky.
The problem is that:
a) To be able to tell which you need you need the pagesize of the
area
b) Then you need the fd if it is a hugepage
(You can get (a) from (b) by a syscall we already do once)
c) If it's normal RAM you need the memory address but...
d) If it's a hugepage you need the offset in the file
which is a mess; so you either have to pass all those parameters,
or end up passing a RAMBlock* which doesn't feel like it should
make its way into any of the os-* files.
I could move it to exec.c that already has some ifdef on OSs;
what do you think?
Dave
> For the rest, I am ok with it.
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
[Qemu-devel] [PATCH 04/15] Fold postcopy_ram_discard_range into ram_discard_range, Dr. David Alan Gilbert (git), 2017/01/06
[Qemu-devel] [PATCH 03/15] postcopy: Chunk discards for hugepages, Dr. David Alan Gilbert (git), 2017/01/06
[Qemu-devel] [PATCH 06/15] postcopy: Record largest page size, Dr. David Alan Gilbert (git), 2017/01/06