From: Linus Torvalds <torvalds@linux-foundation.org>
To: Michal Hocko <mhocko@kernel.org>
Cc: wei.w.wang@intel.com, virtio-dev@lists.oasis-open.org,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
virtualization <virtualization@lists.linux-foundation.org>,
KVM list <kvm@vger.kernel.org>, linux-mm <linux-mm@kvack.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
Andrew Morton <akpm@linux-foundation.org>,
Paolo Bonzini <pbonzini@redhat.com>,
liliang.opensource@gmail.com, yang.zhang.wz@gmail.com,
quan.xu0@gmail.com, nilal@redhat.com,
Rik van Riel <riel@redhat.com>,
peterx@redhat.com
Subject: Re: [PATCH v35 1/5] mm: support to get hints of free page blocks
Date: Wed, 11 Jul 2018 09:23:54 -0700 [thread overview]
Message-ID: <CA+55aFwku2tDH4+rfaC67xc4-cEwSrXgnQaci=e2id5ZCRE9JQ@mail.gmail.com> (raw)
In-Reply-To: <20180711092152.GE20050@dhcp22.suse.cz>
On Wed, Jul 11, 2018 at 2:21 AM Michal Hocko <mhocko@kernel.org> wrote:
>
> We already have an interface for that. alloc_pages(GFP_NOWAIT, MAX_ORDER -1).
> So why do we need any array based interface?
That was actually my original argument in the original thread - that
the only new interface people might want is one that just tells how
many of those MAX_ORDER-1 pages there are.
See the thread in v33 with the subject
"[PATCH v33 1/4] mm: add a function to get free page blocks"
and look for me suggesting just using
#define GFP_MINFLAGS (__GFP_NORETRY | __GFP_NOWARN |
__GFP_THISNODE | __GFP_NOMEMALLOC)
struct page *page = alloc_pages(GFP_MINFLAGS, MAX_ORDER-1);
for this all.
But I could also see an argument for "allocate N pages of size
MAX_ORDER-1", with some small N, simply because I can see the
advantage of not taking and releasing the locking and looking up the
zone individually N times.
If you want to get gigabytes of memory (or terabytes), doing it in
bigger chunks than one single maximum-sized page sounds fairly
reasonable.
I just don't think that "thousands of pages" is reasonable. But "tens
of max-sized pages" sounds fair enough to me, and it would certainly
not be a pain for the VM.
So I'm open to new interfaces. I just want those new interfaces to
make sense, and be low latency and simple for the VM to do. I'm
objecting to the incredibly baroque and heavy-weight one that can
return near-infinite amounts of memory.
The real advantage of jjuist the existing "alloc_pages()" model is
that I think the ballooning people can use that to *test* things out.
If it turns out that taking and releasing the VM locks is a big cost,
we can see if a batch interface that allows you to get tens of pages
at the same time is worth it.
So yes, I'd suggest starting with just the existing alloc_pages. Maybe
it's not enough, but it should be good enough for testing.
Linus
next prev parent reply other threads:[~2018-07-11 16:24 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-07-10 9:31 [PATCH v35 0/5] Virtio-balloon: support free page reporting Wei Wang
2018-07-10 9:31 ` [PATCH v35 1/5] mm: support to get hints of free page blocks Wei Wang
2018-07-10 10:16 ` Wang, Wei W
2018-07-10 17:33 ` Linus Torvalds
2018-07-11 1:28 ` Wei Wang
2018-07-11 1:44 ` Linus Torvalds
2018-07-11 9:21 ` Michal Hocko
2018-07-11 10:52 ` Wei Wang
2018-07-11 11:09 ` Michal Hocko
2018-07-11 13:55 ` Wang, Wei W
2018-07-11 14:38 ` Michal Hocko
2018-07-11 19:36 ` Michael S. Tsirkin
2018-07-11 16:23 ` Linus Torvalds [this message]
2018-07-12 2:21 ` Wei Wang
2018-07-12 2:30 ` Linus Torvalds
2018-07-12 2:52 ` Wei Wang
2018-07-12 8:13 ` Michal Hocko
2018-07-12 11:34 ` Wei Wang
2018-07-12 11:49 ` Michal Hocko
2018-07-13 0:33 ` Wei Wang
2018-07-12 13:12 ` Michal Hocko
2018-07-11 4:00 ` Michael S. Tsirkin
2018-07-11 4:04 ` Michael S. Tsirkin
2018-07-10 9:31 ` [PATCH v35 2/5] virtio-balloon: remove BUG() in init_vqs Wei Wang
2018-07-10 9:31 ` [PATCH v35 3/5] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT Wei Wang
2018-07-10 9:31 ` [PATCH v35 4/5] mm/page_poison: expose page_poisoning_enabled to kernel modules Wei Wang
2018-07-10 9:31 ` [PATCH v35 5/5] virtio-balloon: VIRTIO_BALLOON_F_PAGE_POISON Wei Wang
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