From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: wei.w.wang@intel.com
Cc: virtio-dev@lists.oasis-open.org, linux-kernel@vger.kernel.org,
qemu-devel@nongnu.org, virtualization@lists.linux-foundation.org,
kvm@vger.kernel.org, linux-mm@kvack.org, mst@redhat.com,
mhocko@kernel.org, akpm@linux-foundation.org,
mawilcox@microsoft.com, david@redhat.com,
cornelia.huck@de.ibm.com, mgorman@techsingularity.net,
aarcange@redhat.com, amit.shah@redhat.com, pbonzini@redhat.com,
willy@infradead.org, liliang.opensource@gmail.com,
yang.zhang.wz@gmail.com, quan.xu@aliyun.com, nilal@redhat.com,
riel@redhat.com
Subject: Re: [PATCH v18 05/10] xbitmap: add more operations
Date: Thu, 30 Nov 2017 19:34:10 +0900 [thread overview]
Message-ID: <201711301934.CDC21800.FSLtJFFOOVQHMO@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <1511963726-34070-6-git-send-email-wei.w.wang@intel.com>
Wei Wang wrote:
> /**
> + * xb_clear_bit - clear a range of bits in the xbitmap
Name mismatch.
> + * @start: the start of the bit range, inclusive
> + * @end: the end of the bit range, inclusive
> + *
> + * This function is used to clear a bit in the xbitmap. If all the bits of the
> + * bitmap are 0, the bitmap will be freed.
> + */
> +void xb_clear_bit_range(struct xb *xb, unsigned long start, unsigned long end)
> +{
> + struct radix_tree_root *root = &xb->xbrt;
> + struct radix_tree_node *node;
> + void **slot;
> + struct ida_bitmap *bitmap;
> + unsigned int nbits;
> +
> + for (; start < end; start = (start | (IDA_BITMAP_BITS - 1)) + 1) {
> + unsigned long index = start / IDA_BITMAP_BITS;
> + unsigned long bit = start % IDA_BITMAP_BITS;
> +
> + bitmap = __radix_tree_lookup(root, index, &node, &slot);
> + if (radix_tree_exception(bitmap)) {
> + unsigned long ebit = bit + 2;
> + unsigned long tmp = (unsigned long)bitmap;
> +
> + nbits = min(end - start + 1, BITS_PER_LONG - ebit);
"nbits = min(end - start + 1," seems to expect that start == end is legal
for clearing only 1 bit. But this function is no-op if start == end.
Please clarify what "inclusive" intended.
> +
> + if (ebit >= BITS_PER_LONG)
> + continue;
(I don't understand how radix tree works, but generally this patchset looks fuzzy
to me about boundary cases. Thus, I want to confirm that this is not an overlook.)
Why is making "ebit >= BITS_PER_LONG" (e.g. start == 62) case a no-op correct?
Aren't there bits which should have been cleared in this case?
> + bitmap_clear(&tmp, ebit, nbits);
> + if (tmp == RADIX_TREE_EXCEPTIONAL_ENTRY)
> + __radix_tree_delete(root, node, slot);
> + else
> + rcu_assign_pointer(*slot, (void *)tmp);
> + } else if (bitmap) {
> + nbits = min(end - start + 1, IDA_BITMAP_BITS - bit);
> +
> + if (nbits != IDA_BITMAP_BITS)
> + bitmap_clear(bitmap->bitmap, bit, nbits);
> +
> + if (nbits == IDA_BITMAP_BITS ||
> + bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) {
> + kfree(bitmap);
> + __radix_tree_delete(root, node, slot);
> + }
> + }
> + }
> +}
> +static inline __always_inline void bitmap_clear(unsigned long *map,
> + unsigned int start,
> + unsigned int nbits)
> +{
> + if (__builtin_constant_p(nbits) && nbits == 1)
> + __clear_bit(start, map);
> + else if (__builtin_constant_p(start & 7) && IS_ALIGNED(start, 8) &&
> + __builtin_constant_p(nbits & 7) && IS_ALIGNED(nbits, 8))
It looks strange to apply __builtin_constant_p test to variables after "& 7".
> + memset((char *)map + start / 8, 0, nbits / 8);
> + else
> + __bitmap_clear(map, start, nbits);
> +}
> +
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next prev parent reply other threads:[~2017-11-30 10:35 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-11-29 13:55 [PATCH v18 00/10] Virtio-balloon Enhancement Wei Wang
2017-11-29 13:55 ` [PATCH v18 01/10] idr: add #include <linux/bug.h> Wei Wang
2017-11-30 0:58 ` Matthew Wilcox
2017-11-30 7:07 ` Michal Hocko
2017-11-30 21:49 ` Andrew Morton
2017-11-29 13:55 ` [PATCH v18 02/10] radix tree test suite: remove ARRAY_SIZE to avoid redefinition Wei Wang
2017-11-29 13:55 ` [PATCH v18 03/10] xbitmap: Introduce xbitmap Wei Wang
2017-11-29 13:55 ` [PATCH v18 04/10] xbitmap: potential improvement Wei Wang
2017-11-29 13:55 ` [PATCH v18 05/10] xbitmap: add more operations Wei Wang
2017-11-30 10:34 ` Tetsuo Handa [this message]
2017-11-30 13:35 ` Tetsuo Handa
2017-11-30 14:39 ` Matthew Wilcox
2017-12-03 1:44 ` Tetsuo Handa
2017-12-01 8:02 ` Wei Wang
2017-12-01 13:02 ` Tetsuo Handa
2017-12-01 14:13 ` Matthew Wilcox
2017-12-01 15:09 ` Wang, Wei W
2017-12-01 17:25 ` Matthew Wilcox
2017-12-03 1:50 ` Tetsuo Handa
2017-12-07 12:01 ` Wei Wang
2017-12-07 15:41 ` Michael S. Tsirkin
2017-11-29 13:55 ` [PATCH v18 06/10] virtio_ring: add a new API, virtqueue_add_one_desc Wei Wang
2017-11-30 19:38 ` Michael S. Tsirkin
2017-12-01 8:06 ` Wei Wang
2017-11-29 13:55 ` [PATCH v18 07/10] virtio-balloon: VIRTIO_BALLOON_F_SG Wei Wang
2017-11-30 10:35 ` Tetsuo Handa
2017-11-30 16:25 ` Wang, Wei W
2017-12-01 15:38 ` Michael S. Tsirkin
2017-12-04 3:46 ` Wei Wang
2017-11-29 13:55 ` [PATCH v18 08/10] mm: support reporting free page blocks Wei Wang
2017-11-29 13:55 ` [PATCH v18 09/10] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ Wei Wang
2017-11-29 13:55 ` [PATCH v18 10/10] virtio-balloon: don't report free pages when page poisoning is enabled Wei Wang
2017-11-30 10:45 ` Tetsuo Handa
2017-12-01 8:06 ` Wei Wang
2017-12-01 15:49 ` Michael S. Tsirkin
2017-12-04 5:39 ` Wei Wang
2017-12-11 6:38 ` Wei Wang
2017-12-11 13:24 ` Michael S. Tsirkin
2017-12-12 12:21 ` Wei Wang
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