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Re: [Qemu-devel] [PATCH 05/15] postcopy: enhance ram_discard_range for h
From: |
Juan Quintela |
Subject: |
Re: [Qemu-devel] [PATCH 05/15] postcopy: enhance ram_discard_range for hugepages |
Date: |
Mon, 30 Jan 2017 20:19:06 +0100 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) |
"Dr. David Alan Gilbert" <address@hidden> wrote:
> * 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>
>> > +#if defined(CONFIG_FALLOCATE_PUNCH_HOLE)
>> > +#include <linux/falloc.h>
>> > +#endif
I hate this in generic code :-()
I think that the function will have to be called:
qemu_ram_punch_hole(RAMBblock *, length);
Put it all together at the beggining of the file?
What I don't want is that if someone arrives with a way to do this in
other OS, we need to put yet more ifdefs. I preffer very much that it
just have to define a function with that semantics. Agreed that this is
a mess, but I can't think of an easier way of doing it either :-()
>> > @@ -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
- Re: [Qemu-devel] [PATCH 01/15] postcopy: Transmit and compare individual page sizes, (continued)
[Qemu-devel] [PATCH 02/15] postcopy: Transmit ram size summary word, Dr. David Alan Gilbert (git), 2017/01/06
[Qemu-devel] [PATCH 05/15] postcopy: enhance ram_discard_range for hugepages, Dr. David Alan Gilbert (git), 2017/01/06
[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
[Qemu-devel] [PATCH 08/15] postcopy: Use temporary for placing zero huge pages, Dr. David Alan Gilbert (git), 2017/01/06