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Date: Mon, 11 Sep 2017 05:54:56 -0700
From: Matthew Wilcox <willy@...radead.org>
To: Wei Wang <wei.w.wang@...el.com>
Cc: virtio-dev@...ts.oasis-open.org, linux-kernel@...r.kernel.org,
qemu-devel@...gnu.org, virtualization@...ts.linux-foundation.org,
kvm@...r.kernel.org, linux-mm@...ck.org, mst@...hat.com,
mhocko@...nel.org, akpm@...ux-foundation.org,
mawilcox@...rosoft.com, david@...hat.com, cornelia.huck@...ibm.com,
mgorman@...hsingularity.net, aarcange@...hat.com,
amit.shah@...hat.com, pbonzini@...hat.com,
liliang.opensource@...il.com, yang.zhang.wz@...il.com,
quan.xu@...yun.com
Subject: Re: [PATCH v15 1/5] lib/xbitmap: Introduce xbitmap
On Mon, Aug 28, 2017 at 06:08:29PM +0800, Wei Wang wrote:
> From: Matthew Wilcox <mawilcox@...rosoft.com>
>
> The eXtensible Bitmap is a sparse bitmap representation which is
> efficient for set bits which tend to cluster. It supports up to
> 'unsigned long' worth of bits, and this commit adds the bare bones --
> xb_set_bit(), xb_clear_bit() and xb_test_bit().
>
> Signed-off-by: Matthew Wilcox <mawilcox@...rosoft.com>
> Signed-off-by: Wei Wang <wei.w.wang@...el.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: Michael S. Tsirkin <mst@...hat.com>
This is quite naughty of you. You've modified the xbitmap implementation
without any indication in the changelog that you did so. I don't
think the modifications you made are an improvement, but without any
argumentation from you I don't know why you think they're an improvement.
> diff --git a/lib/radix-tree.c b/lib/radix-tree.c
> index 898e879..ee72e2c 100644
> --- a/lib/radix-tree.c
> +++ b/lib/radix-tree.c
> @@ -496,6 +496,7 @@ static int __radix_tree_preload(gfp_t gfp_mask, unsigned nr)
> out:
> return ret;
> }
> +EXPORT_SYMBOL(__radix_tree_preload);
>
> /*
> * Load up this CPU's radix_tree_node buffer with sufficient objects to
You exported this to modules for some reason. Why?
> @@ -2003,6 +2018,7 @@ static bool __radix_tree_delete(struct radix_tree_root *root,
> replace_slot(slot, NULL, node, -1, exceptional);
> return node && delete_node(root, node, NULL, NULL);
> }
> +EXPORT_SYMBOL(__radix_tree_delete);
>
> /**
> * radix_tree_iter_delete - delete the entry at this iterator position
Ditto?
> diff --git a/lib/xbitmap.c b/lib/xbitmap.c
> new file mode 100644
> index 0000000..8c55296
> --- /dev/null
> +++ b/lib/xbitmap.c
> @@ -0,0 +1,176 @@
> +#include <linux/slab.h>
> +#include <linux/xbitmap.h>
> +
> +/*
> + * The xbitmap implementation supports up to ULONG_MAX bits, and it is
> + * implemented based on ida bitmaps. So, given an unsigned long index,
> + * the high order XB_INDEX_BITS bits of the index is used to find the
> + * corresponding item (i.e. ida bitmap) from the radix tree, and the low
> + * order (i.e. ilog2(IDA_BITMAP_BITS)) bits of the index are indexed into
> + * the ida bitmap to find the bit.
> + */
> +#define XB_INDEX_BITS (BITS_PER_LONG - ilog2(IDA_BITMAP_BITS))
> +#define XB_MAX_PATH (DIV_ROUND_UP(XB_INDEX_BITS, \
> + RADIX_TREE_MAP_SHIFT))
> +#define XB_PRELOAD_SIZE (XB_MAX_PATH * 2 - 1)
I don't understand why you moved the xb_preload code here from the
radix tree. I want all the code which touches the preload implementation
together in one place, which is the radix tree.
> +enum xb_ops {
> + XB_SET,
> + XB_CLEAR,
> + XB_TEST
> +};
> +
> +static int xb_bit_ops(struct xb *xb, unsigned long bit, enum xb_ops ops)
> +{
> + int ret = 0;
> + unsigned long index = bit / IDA_BITMAP_BITS;
> + struct radix_tree_root *root = &xb->xbrt;
> + struct radix_tree_node *node;
> + void **slot;
> + struct ida_bitmap *bitmap;
> + unsigned long ebit, tmp;
> +
> + bit %= IDA_BITMAP_BITS;
> + ebit = bit + RADIX_TREE_EXCEPTIONAL_SHIFT;
> +
> + switch (ops) {
> + case XB_SET:
> + ret = __radix_tree_create(root, index, 0, &node, &slot);
> + if (ret)
> + return ret;
> + bitmap = rcu_dereference_raw(*slot);
> + if (radix_tree_exception(bitmap)) {
> + tmp = (unsigned long)bitmap;
> + if (ebit < BITS_PER_LONG) {
> + tmp |= 1UL << ebit;
> + rcu_assign_pointer(*slot, (void *)tmp);
> + return 0;
> + }
> + bitmap = this_cpu_xchg(ida_bitmap, NULL);
> + if (!bitmap)
> + return -EAGAIN;
> + memset(bitmap, 0, sizeof(*bitmap));
> + bitmap->bitmap[0] =
> + tmp >> RADIX_TREE_EXCEPTIONAL_SHIFT;
> + rcu_assign_pointer(*slot, bitmap);
> + }
> + if (!bitmap) {
> + if (ebit < BITS_PER_LONG) {
> + bitmap = (void *)((1UL << ebit) |
> + RADIX_TREE_EXCEPTIONAL_ENTRY);
> + __radix_tree_replace(root, node, slot, bitmap,
> + NULL, NULL);
> + return 0;
> + }
> + bitmap = this_cpu_xchg(ida_bitmap, NULL);
> + if (!bitmap)
> + return -EAGAIN;
> + memset(bitmap, 0, sizeof(*bitmap));
> + __radix_tree_replace(root, node, slot, bitmap, NULL,
> + NULL);
> + }
> + __set_bit(bit, bitmap->bitmap);
> + break;
> + case XB_CLEAR:
> + bitmap = __radix_tree_lookup(root, index, &node, &slot);
> + if (radix_tree_exception(bitmap)) {
> + tmp = (unsigned long)bitmap;
> + if (ebit >= BITS_PER_LONG)
> + return 0;
> + tmp &= ~(1UL << ebit);
> + if (tmp == RADIX_TREE_EXCEPTIONAL_ENTRY)
> + __radix_tree_delete(root, node, slot);
> + else
> + rcu_assign_pointer(*slot, (void *)tmp);
> + return 0;
> + }
> + if (!bitmap)
> + return 0;
> + __clear_bit(bit, bitmap->bitmap);
> + if (bitmap_empty(bitmap->bitmap, IDA_BITMAP_BITS)) {
> + kfree(bitmap);
> + __radix_tree_delete(root, node, slot);
> + }
> + break;
> + case XB_TEST:
> + bitmap = radix_tree_lookup(root, index);
> + if (!bitmap)
> + return 0;
> + if (radix_tree_exception(bitmap)) {
> + if (ebit > BITS_PER_LONG)
> + return 0;
> + return (unsigned long)bitmap & (1UL << bit);
> + }
> + ret = test_bit(bit, bitmap->bitmap);
> + break;
> + default:
> + return -EINVAL;
> + }
> + return ret;
> +}
This is what I have the biggest problem with. You've spliced
three functions together into a single 86-line function. All that
they share is the first 11 lines of setup! Go back and read
Documentation/process/coding-style.rst section 6 again.
And you've just deleted the test suite. Test suites are incredibly
important! They keep us from regressing.
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