ping? Is these two patches can be merged into linux-4.19? :'(
Thanks,
Gao Xiang
On 2019/2/26 20:43, Gao Xiang wrote:
> Hi Matthew,
>
> On 2019/2/26 13:14, Gao Xiang wrote:
>> From: Matthew Wilcox <willy@xxxxxxxxxxxxx>
>>
>> commit 3159f943aafdbacb2f94c38fdaadabf2bbde2a14 upstream.
>>
>> Introduce xarray value entries and tagged pointers to replace radix
>> tree exceptional entries. This is a slight change in encoding to allow
>> the use of an extra bit (we can now store BITS_PER_LONG - 1 bits in a
>> value entry). It is also a change in emphasis; exceptional entries are
>> intimidating and different. As the comment explains, you can choose
>> to store values or pointers in the xarray and they are both first-class
>> citizens.
>>
>> Signed-off-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
>> Reviewed-by: Josef Bacik <jbacik@xxxxxx>
>> [ take the minimum subset of tagged pointer support only. ]
>> Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
>> Signed-off-by: Gao Xiang <gaoxiang25@xxxxxxxxxx>
>> ---
>> change log v2:
>> - fix tagged pointer apis to make it work properly pointed out by Matthew;
>
> Is this version ok? Could you kindly give an "Acked-by" tag for this patch?
>
> The following patch is important for erofs, I'd like to backport it ASAP...
> staging: erofs: fix race when the managed cache is enabled
>
> It will be of great help. Thanks in advance!
>
> Thanks,
> Gao Xiang
>
>>
>> drivers/staging/erofs/utils.c | 18 +++++----------
>> include/linux/xarray.h | 52 +++++++++++++++++++++++++++++++++++++++++++
>> 2 files changed, 58 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/staging/erofs/utils.c b/drivers/staging/erofs/utils.c
>> index 595cf90af9bb..bdee9bd09f11 100644
>> --- a/drivers/staging/erofs/utils.c
>> +++ b/drivers/staging/erofs/utils.c
>> @@ -35,7 +35,6 @@ static atomic_long_t erofs_global_shrink_cnt;
>>
>> #ifdef CONFIG_EROFS_FS_ZIP
>>
>> -/* radix_tree and the future XArray both don't use tagptr_t yet */
>> struct erofs_workgroup *erofs_find_workgroup(
>> struct super_block *sb, pgoff_t index, bool *tag)
>> {
>> @@ -47,9 +46,8 @@ struct erofs_workgroup *erofs_find_workgroup(
>> rcu_read_lock();
>> grp = radix_tree_lookup(&sbi->workstn_tree, index);
>> if (grp != NULL) {
>> - *tag = radix_tree_exceptional_entry(grp);
>> - grp = (void *)((unsigned long)grp &
>> - ~RADIX_TREE_EXCEPTIONAL_ENTRY);
>> + *tag = xa_pointer_tag(grp);
>> + grp = xa_untag_pointer(grp);
>>
>> if (erofs_workgroup_get(grp, &oldcount)) {
>> /* prefer to relax rcu read side */
>> @@ -83,9 +81,7 @@ int erofs_register_workgroup(struct super_block *sb,
>> sbi = EROFS_SB(sb);
>> erofs_workstn_lock(sbi);
>>
>> - if (tag)
>> - grp = (void *)((unsigned long)grp |
>> - 1UL << RADIX_TREE_EXCEPTIONAL_SHIFT);
>> + grp = xa_tag_pointer(grp, tag);
>>
>> err = radix_tree_insert(&sbi->workstn_tree,
>> grp->index, grp);
>> @@ -131,9 +127,7 @@ unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
>>
>> for (i = 0; i < found; ++i) {
>> int cnt;
>> - struct erofs_workgroup *grp = (void *)
>> - ((unsigned long)batch[i] &
>> - ~RADIX_TREE_EXCEPTIONAL_ENTRY);
>> + struct erofs_workgroup *grp = xa_untag_pointer(batch[i]);
>>
>> first_index = grp->index + 1;
>>
>> @@ -150,8 +144,8 @@ unsigned long erofs_shrink_workstation(struct erofs_sb_info *sbi,
>> #endif
>> continue;
>>
>> - if (radix_tree_delete(&sbi->workstn_tree,
>> - grp->index) != grp) {
>> + if (xa_untag_pointer(radix_tree_delete(&sbi->workstn_tree,
>> + grp->index)) != grp) {
>> #ifdef EROFS_FS_HAS_MANAGED_CACHE
>> skip:
>> erofs_workgroup_unfreeze(grp, 1);
>> diff --git a/include/linux/xarray.h b/include/linux/xarray.h
>> index 2dfc8006fe64..51ae9779d08b 100644
>> --- a/include/linux/xarray.h
>> +++ b/include/linux/xarray.h
>> @@ -9,6 +9,58 @@
>>
>> #include <linux/spinlock.h>
>>
>> +/**
>> + * 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)
>> +{
>> + if (__builtin_constant_p(tag))
>> + BUILD_BUG_ON(tag > 1);
>> + else
>> + BUG_ON(tag > 1);
>> + return (void *)((unsigned long)p | (tag << 1));
>> +}
>> +
>> +/**
>> + * xa_untag_pointer() - Turn an XArray entry into a plain pointer.
>> + * @entry: XArray entry.
>> + *
>> + * If you have stored a tagged pointer in the XArray, call this function
>> + * to get the untagged version of the pointer.
>> + *
>> + * Context: Any context.
>> + * Return: A pointer.
>> + */
>> +static inline void *xa_untag_pointer(void *entry)
>> +{
>> + return (void *)((unsigned long)entry & ~3UL);
>> +}
>> +
>> +/**
>> + * xa_pointer_tag() - Get the tag stored in an XArray entry.
>> + * @entry: XArray entry.
>> + *
>> + * If you have stored a tagged pointer in the XArray, call this function
>> + * to get the tag of that pointer.
>> + *
>> + * Context: Any context.
>> + * Return: A tag.
>> + */
>> +static inline unsigned int xa_pointer_tag(void *entry)
>> +{
>> + return ((unsigned long)entry & 3UL) >> 1;
>> +}
>> +
>> #define xa_trylock(xa) spin_trylock(&(xa)->xa_lock)
>> #define xa_lock(xa) spin_lock(&(xa)->xa_lock)
>> #define xa_unlock(xa) spin_unlock(&(xa)->xa_lock)
>>
