From: Matthew Wilcox <willy@infradead.org>
To: Wei Wang <wei.w.wang@intel.com>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>,
"virtio-dev@lists.oasis-open.org"
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Subject: Re: [PATCH v19 3/7] xbitmap: add more operations
Date: Sun, 17 Dec 2017 18:59:27 -0800 [thread overview]
Message-ID: <20171218025927.GB6683@bombadil.infradead.org> (raw)
In-Reply-To: <5A3728DC.3060509@intel.com>
On Mon, Dec 18, 2017 at 10:33:00AM +0800, Wei Wang wrote:
> > My only qualm is that I've been considering optimising the memory
> > consumption when an entire 1024-bit chunk is full; instead of keeping a
> > pointer to a 128-byte entry full of ones, store a special value in the
> > radix tree which means "every bit is set".
> >
> > The downside is that we then have to pass GFP flags to xbit_clear() and
> > xbit_zero(), and they can fail. It's not clear to me whether that's a
> > good tradeoff.
>
> Yes, this will sacrifice performance. In many usages, users may set bits one
> by one, and each time when a bit is set, it needs to scan the whole
> ida_bitmap to see if all other bits are set, if so, it can free the
> ida_bitmap. I think this extra scanning of the ida_bitmap would add a lot
> overhead.
Not a huge amount of overhead. An ida_bitmap is only two cachelines,
and the loop is simply 'check each word against ~0ul', so up to 16
load/test/loop instructions. Plus we have to do that anyway to maintain
the free tag for IDAs.
> > But I need to get the XArray (which replaces the radix tree) finished first.
>
> OK. It seems the new implementation wouldn't be done shortly.
> Other parts of this patch series are close to the end of review, and we hope
> to make some progress soon. Would it be acceptable that we continue with the
> basic xb_ implementation (e.g. as xbitmap 1.0) for this patch series? and
> xbit_ implementation can come as xbitmap 2.0 in the future?
Yes, absolutely, I don't want to hold you up behind the XArray.
next prev parent reply other threads:[~2017-12-18 2:59 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-12-12 11:55 [PATCH v19 0/7] Virtio-balloon Enhancement Wei Wang
2017-12-12 11:55 ` [PATCH v19 1/7] xbitmap: Introduce xbitmap Wei Wang
2017-12-12 12:53 ` Philippe Ombredanne
2017-12-15 11:05 ` kbuild test robot
2017-12-15 13:24 ` Matthew Wilcox
2017-12-16 10:10 ` Wei Wang
2017-12-12 11:55 ` [PATCH v19 2/7] xbitmap: potential improvement Wei Wang
2017-12-15 3:07 ` kbuild test robot
2017-12-12 11:55 ` [PATCH v19 3/7] xbitmap: add more operations Wei Wang
2017-12-12 13:20 ` Tetsuo Handa
2017-12-13 12:26 ` Wei Wang
2017-12-13 14:16 ` Tetsuo Handa
2017-12-14 3:47 ` Wei Wang
2017-12-14 11:47 ` [virtio-dev] " Wei Wang
2017-12-14 16:29 ` Tetsuo Handa
2017-12-14 18:12 ` Matthew Wilcox
2017-12-15 16:21 ` Tetsuo Handa
2017-12-15 18:26 ` Michael S. Tsirkin
2017-12-16 4:31 ` Tetsuo Handa
2017-12-16 5:05 ` Matthew Wilcox
2017-12-16 5:57 ` Tetsuo Handa
2017-12-15 18:49 ` Matthew Wilcox
2017-12-15 19:22 ` Matthew Wilcox
2017-12-17 13:47 ` Wang, Wei W
2017-12-17 22:18 ` Matthew Wilcox
2017-12-18 2:33 ` Wei Wang
2017-12-18 2:59 ` Matthew Wilcox [this message]
2017-12-16 10:14 ` Wei Wang
2017-12-14 12:37 ` Matthew Wilcox
2017-12-15 18:42 ` Matthew Wilcox
2017-12-16 10:12 ` Wei Wang
2017-12-16 11:28 ` Tetsuo Handa
2017-12-17 5:24 ` Wei Wang
2017-12-17 10:21 ` Tetsuo Handa
2017-12-17 11:50 ` Wang, Wei W
2017-12-17 15:16 ` Tetsuo Handa
2017-12-18 8:05 ` Wei Wang
2017-12-12 11:55 ` [PATCH v19 4/7] virtio-balloon: VIRTIO_BALLOON_F_SG Wei Wang
2017-12-12 11:55 ` [PATCH v19 5/7] mm: support reporting free page blocks Wei Wang
2017-12-12 11:55 ` [PATCH v19 6/7] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ Wei Wang
2017-12-12 11:55 ` [PATCH v19 7/7] virtio-balloon: don't report free pages when page poisoning is enabled Wei Wang
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