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From: Matthew Wilcox <willy@infradead.org>
To: Gao Xiang <hsiangkao@aol.com>
Cc: stable@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	linux-erofs@lists.ozlabs.org, Chao Yu <yuchao0@huawei.com>,
	Gao Xiang <gaoxiang25@huawei.com>
Subject: Re: [PATCH for-4.19 1/2] xarray: Replace exceptional entries
Date: Mon, 25 Feb 2019 10:27:54 -0800	[thread overview]
Message-ID: <20190225182754.GF2496@bombadil.infradead.org> (raw)
In-Reply-To: <20190225175809.13427-1-hsiangkao@aol.com>

On Tue, Feb 26, 2019 at 01:58:08AM +0800, Gao Xiang wrote:
> +/**
> + * xa_tag_pointer() - Create an XArray entry for a tagged pointer.
> + * @p: Plain pointer.
> + * @tag: Tag value (0, 1 or 3).
> + *
> + * If the user of the XArray prefers, they can tag their pointers instead
> + * of storing value entries.  Three tags are available (0, 1 and 3).
> + * These are distinct from the xa_mark_t as they are not replicated up
> + * through the array and cannot be searched for.
> + *
> + * Context: Any context.
> + * Return: An XArray entry.
> + */
> +static inline void *xa_tag_pointer(void *p, unsigned long tag)
> +{
> +	return (void *)((unsigned long)p | tag);
> +}

I think we have to diverge from upstream here.  Part of the original
commit is changing the format of internal & exceptional entries to give
us an extra bit.  This implementation of xa_tag_pointer would transform
a pointer tagged with value 1 into an internal pointer, which would
break the radix tree.

I would suggest:

+/**
+ * xa_tag_pointer() - Create an XArray entry for a tagged pointer.
+ * @p: Plain pointer.
+ * @tag: Tag value (0 or 1).
+ *
+ * If the user of the XArray prefers, they can tag their pointers instead
+ * of storing value entries.  Two tags are available (0 and 1).
+ * These are distinct from the xa_mark_t as they are not replicated up
+ * through the array and cannot be searched for.
+ *
+ * Context: Any context.
+ * Return: An XArray entry.
+ */
+static inline void *xa_tag_pointer(void *p, unsigned long tag)
+{
+	BUG_ON(tag > 1);
+	return (void *)((unsigned long)p | (tag << 1));
+}

xa_untag_pointer() and xa_pointer_tag() will need corresponding changes.

WARNING: multiple messages have this Message-ID (diff)
From: willy@infradead.org (Matthew Wilcox)
Subject: [PATCH for-4.19 1/2] xarray: Replace exceptional entries
Date: Mon, 25 Feb 2019 10:27:54 -0800	[thread overview]
Message-ID: <20190225182754.GF2496@bombadil.infradead.org> (raw)
In-Reply-To: <20190225175809.13427-1-hsiangkao@aol.com>

On Tue, Feb 26, 2019@01:58:08AM +0800, Gao Xiang wrote:
> +/**
> + * xa_tag_pointer() - Create an XArray entry for a tagged pointer.
> + * @p: Plain pointer.
> + * @tag: Tag value (0, 1 or 3).
> + *
> + * If the user of the XArray prefers, they can tag their pointers instead
> + * of storing value entries.  Three tags are available (0, 1 and 3).
> + * These are distinct from the xa_mark_t as they are not replicated up
> + * through the array and cannot be searched for.
> + *
> + * Context: Any context.
> + * Return: An XArray entry.
> + */
> +static inline void *xa_tag_pointer(void *p, unsigned long tag)
> +{
> +	return (void *)((unsigned long)p | tag);
> +}

I think we have to diverge from upstream here.  Part of the original
commit is changing the format of internal & exceptional entries to give
us an extra bit.  This implementation of xa_tag_pointer would transform
a pointer tagged with value 1 into an internal pointer, which would
break the radix tree.

I would suggest:

+/**
+ * xa_tag_pointer() - Create an XArray entry for a tagged pointer.
+ * @p: Plain pointer.
+ * @tag: Tag value (0 or 1).
+ *
+ * If the user of the XArray prefers, they can tag their pointers instead
+ * of storing value entries.  Two tags are available (0 and 1).
+ * These are distinct from the xa_mark_t as they are not replicated up
+ * through the array and cannot be searched for.
+ *
+ * Context: Any context.
+ * Return: An XArray entry.
+ */
+static inline void *xa_tag_pointer(void *p, unsigned long tag)
+{
+	BUG_ON(tag > 1);
+	return (void *)((unsigned long)p | (tag << 1));
+}

xa_untag_pointer() and xa_pointer_tag() will need corresponding changes.

  parent reply	other threads:[~2019-02-25 18:27 UTC|newest]

Thread overview: 68+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-20  9:18 [PATCH for-4.19 00/12] erofs fixes for linux-4.19.y Gao Xiang
2019-02-20  9:18 ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 01/12] staging: erofs: fix a bug when appling cache strategy Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 02/12] staging: erofs: complete error handing of z_erofs_do_read_page Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-25 14:59   ` Greg Kroah-Hartman
2019-02-25 14:59     ` Greg Kroah-Hartman
2019-02-25 15:04     ` Gao Xiang
2019-02-25 15:04       ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 03/12] staging: erofs: replace BUG_ON with DBG_BUGON in data.c Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 04/12] staging: erofs: drop multiref support temporarily Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 05/12] staging: erofs: remove the redundant d_rehash() for the root dentry Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 06/12] staging: erofs: fix race when the managed cache is enabled Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-25 15:04   ` Greg Kroah-Hartman
2019-02-25 15:04     ` Greg Kroah-Hartman
2019-02-25 15:07     ` Gao Xiang
2019-02-25 15:07       ` Gao Xiang
2019-02-25 15:51       ` Greg Kroah-Hartman
2019-02-25 15:51         ` Greg Kroah-Hartman
2019-02-25 15:57         ` Gao Xiang
2019-02-25 15:57           ` Gao Xiang
2019-02-25 17:58         ` [PATCH for-4.19 1/2] xarray: Replace exceptional entries Gao Xiang
2019-02-25 17:58           ` Gao Xiang
2019-02-25 17:58           ` [PATCH for-4.19 2/2] staging: erofs: fix race when the managed cache is enabled Gao Xiang
2019-02-25 17:58             ` Gao Xiang
2019-02-25 18:27           ` Matthew Wilcox [this message]
2019-02-25 18:27             ` [PATCH for-4.19 1/2] xarray: Replace exceptional entries Matthew Wilcox
2019-02-26  1:21             ` Gao Xiang
2019-02-26  1:21               ` Gao Xiang
2019-02-26  5:14             ` [PATCH v2 " Gao Xiang
2019-02-26  5:14               ` Gao Xiang
2019-02-26  5:14               ` [PATCH v2 for-4.19 2/2] staging: erofs: fix race when the managed cache is enabled Gao Xiang
2019-02-26  5:14                 ` Gao Xiang
2019-02-26 12:43               ` [PATCH v2 for-4.19 1/2] xarray: Replace exceptional entries Gao Xiang
2019-02-26 12:43                 ` Gao Xiang
2019-03-04  5:13                 ` Gao Xiang
2019-03-04  5:13                   ` Gao Xiang
2019-03-13  9:18                   ` Gao Xiang
2019-03-13  9:18                     ` Gao Xiang
2019-02-25 15:25     ` [PATCH for-4.19 06/12] staging: erofs: fix race when the managed cache is enabled Matthew Wilcox
2019-02-25 15:25       ` Matthew Wilcox
2019-02-25 15:52       ` Greg Kroah-Hartman
2019-02-25 15:52         ` Greg Kroah-Hartman
2019-02-25 16:04         ` Matthew Wilcox
2019-02-25 16:04           ` Matthew Wilcox
2019-02-20  9:18 ` [PATCH for-4.19 07/12] staging: erofs: atomic_cond_read_relaxed on ref-locked workgroup Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 08/12] staging: erofs: fix `erofs_workgroup_{try_to_freeze, unfreeze}' Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 09/12] staging: erofs: add a full barrier in erofs_workgroup_unfreeze Gao Xiang
2019-02-20  9:18   ` Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 10/12] staging: erofs: {dir,inode,super}.c: rectify BUG_ONs Gao Xiang
2019-02-20  9:18   ` [PATCH for-4.19 10/12] staging: erofs: {dir, inode, super}.c: " Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 11/12] staging: erofs: unzip_{pagevec.h,vle.c}: " Gao Xiang
2019-02-20  9:18   ` [PATCH for-4.19 11/12] staging: erofs: unzip_{pagevec.h, vle.c}: " Gao Xiang
2019-02-20  9:18 ` [PATCH for-4.19 12/12] staging: erofs: unzip_vle_lz4.c,utils.c: " Gao Xiang
2019-02-20  9:18   ` [PATCH for-4.19 12/12] staging: erofs: unzip_vle_lz4.c, utils.c: " Gao Xiang
2019-02-22  8:35 ` [PATCH for-4.19 00/12] erofs fixes for linux-4.19.y Greg Kroah-Hartman
2019-02-22  8:35   ` Greg Kroah-Hartman
2019-02-22  9:03   ` Gao Xiang
2019-02-22  9:03     ` Gao Xiang
2019-02-25 15:28 ` Greg Kroah-Hartman
2019-02-25 15:28   ` Greg Kroah-Hartman

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