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Date: Sat, 13 Sep 2014 09:26:49 +0400
From: Konstantin Khlebnikov <koct9i@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: Konstantin Khlebnikov <k.khlebnikov@...sung.com>,
Rafael Aquini <aquini@...hat.com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
"linux-mm@...ck.org" <linux-mm@...ck.org>,
Andrey Ryabinin <ryabinin.a.a@...il.com>,
Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH v2 4/6] mm: introduce common page state for ballooned memory
On Sat, Sep 13, 2014 at 3:51 AM, Andrew Morton
<akpm@...ux-foundation.org> wrote:
> On Sat, 30 Aug 2014 20:41:20 +0400 Konstantin Khlebnikov <koct9i@...il.com> wrote:
>
>> This patch adds page state PageBallon() and functions __Set/ClearPageBalloon.
>> Like PageBuddy() PageBalloon() looks like page-flag but actually this is special
>> state of page->_mapcount counter. There is no conflict because ballooned pages
>> cannot be mapped and cannot be in buddy allocator.
>>
>> Ballooned pages are counted in vmstat counter NR_BALLOON_PAGES, it's shown them
>> in /proc/meminfo and /proc/meminfo. Also this patch it exports PageBallon into
>> userspace via /proc/kpageflags as KPF_BALLOON.
>>
>> All new code is under CONFIG_MEMORY_BALLOON, it should be selected by
>> ballooning driver which wants use this feature.
>
> The delta from the (fixed) v1 is below.
>
> What's up with those Kconfig/Makefile changes? We're now including a
> pile of balloon code into vmlinux when CONFIG_MEMORY_BALLOON=n? These
> changes were not changelogged?
It's been moved into next patch, and not mentioned in changes. Sorry.
>
> Did we really need to put the BalloonPages count into per-zone vmstat,
> global vmstat and /proc/meminfo? Seems a bit overkillish - why so
> important?
Balloon grabs random pages, their distribution among numa nodes might
be important.
But I know nobody who uses numa-aware vm together with ballooning.
Probably it's better to drop per-zone vmstat and line from meminfo,
global vmstat counter should be enough.
>
> Consuming another page flag is a big deal. We keep on nearly running
> out and one day we'll run out for real. page-flags-layout.h is
> incomprehensible. How many flags do we have left (worst-case) with this
> change? Is there no other way? Needs extraordinary justification,
> please.
PageBalloon is not a page flags, it's like PageBuddy -- special state
of _mapcount (-256 in this case).
The same was in v1 and is written in the comment above.
>
> drivers/virtio/Kconfig | 1 -
> include/linux/mm.h | 14 ++++++++++++--
> mm/Makefile | 3 +--
> mm/balloon_compaction.c | 16 ----------------
> 4 files changed, 13 insertions(+), 21 deletions(-)
>
> diff -puN drivers/virtio/Kconfig~mm-introduce-common-page-state-for-ballooned-memory-fix-v2 drivers/virtio/Kconfig
> --- a/drivers/virtio/Kconfig~mm-introduce-common-page-state-for-ballooned-memory-fix-v2
> +++ a/drivers/virtio/Kconfig
> @@ -25,7 +25,6 @@ config VIRTIO_PCI
> config VIRTIO_BALLOON
> tristate "Virtio balloon driver"
> depends on VIRTIO
> - select MEMORY_BALLOON
> ---help---
> This driver supports increasing and decreasing the amount
> of memory within a KVM guest.
> diff -puN include/linux/mm.h~mm-introduce-common-page-state-for-ballooned-memory-fix-v2 include/linux/mm.h
> --- a/include/linux/mm.h~mm-introduce-common-page-state-for-ballooned-memory-fix-v2
> +++ a/include/linux/mm.h
> @@ -561,8 +561,18 @@ static inline int PageBalloon(struct pag
> return IS_ENABLED(CONFIG_MEMORY_BALLOON) &&
> atomic_read(&page->_mapcount) == PAGE_BALLOON_MAPCOUNT_VALUE;
> }
> -void __SetPageBalloon(struct page *page);
> -void __ClearPageBalloon(struct page *page);
> +
> +static inline void __SetPageBalloon(struct page *page)
> +{
> + VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page);
> + atomic_set(&page->_mapcount, PAGE_BALLOON_MAPCOUNT_VALUE);
> +}
> +
> +static inline void __ClearPageBalloon(struct page *page)
> +{
> + VM_BUG_ON_PAGE(!PageBalloon(page), page);
> + atomic_set(&page->_mapcount, -1);
> +}
>
> void put_page(struct page *page);
> void put_pages_list(struct list_head *pages);
> diff -puN mm/Makefile~mm-introduce-common-page-state-for-ballooned-memory-fix-v2 mm/Makefile
> --- a/mm/Makefile~mm-introduce-common-page-state-for-ballooned-memory-fix-v2
> +++ a/mm/Makefile
> @@ -16,7 +16,7 @@ obj-y := filemap.o mempool.o oom_kill.
> readahead.o swap.o truncate.o vmscan.o shmem.o \
> util.o mmzone.o vmstat.o backing-dev.o \
> mm_init.o mmu_context.o percpu.o slab_common.o \
> - compaction.o vmacache.o \
> + compaction.o balloon_compaction.o vmacache.o \
> interval_tree.o list_lru.o workingset.o \
> iov_iter.o $(mmu-y)
>
> @@ -64,4 +64,3 @@ obj-$(CONFIG_ZBUD) += zbud.o
> obj-$(CONFIG_ZSMALLOC) += zsmalloc.o
> obj-$(CONFIG_GENERIC_EARLY_IOREMAP) += early_ioremap.o
> obj-$(CONFIG_CMA) += cma.o
> -obj-$(CONFIG_MEMORY_BALLOON) += balloon_compaction.o
> diff -puN mm/balloon_compaction.c~mm-introduce-common-page-state-for-ballooned-memory-fix-v2 mm/balloon_compaction.c
> --- a/mm/balloon_compaction.c~mm-introduce-common-page-state-for-ballooned-memory-fix-v2
> +++ a/mm/balloon_compaction.c
> @@ -10,22 +10,6 @@
> #include <linux/export.h>
> #include <linux/balloon_compaction.h>
>
> -void __SetPageBalloon(struct page *page)
> -{
> - VM_BUG_ON_PAGE(atomic_read(&page->_mapcount) != -1, page);
> - atomic_set(&page->_mapcount, PAGE_BALLOON_MAPCOUNT_VALUE);
> - inc_zone_page_state(page, NR_BALLOON_PAGES);
> -}
> -EXPORT_SYMBOL(__SetPageBalloon);
> -
> -void __ClearPageBalloon(struct page *page)
> -{
> - VM_BUG_ON_PAGE(!PageBalloon(page), page);
> - atomic_set(&page->_mapcount, -1);
> - dec_zone_page_state(page, NR_BALLOON_PAGES);
> -}
> -EXPORT_SYMBOL(__ClearPageBalloon);
> -
> /*
> * balloon_devinfo_alloc - allocates a balloon device information descriptor.
> * @balloon_dev_descriptor: pointer to reference the balloon device which
> _
>
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