On 2021/1/21 上午9:28, Josef Bacik wrote:

On 1/20/21 7:49 PM, Qu Wenruo wrote:

quoted

On 2021/1/20 下午11:00, Josef Bacik wrote:

quoted

On 1/16/21 2:15 AM, Qu Wenruo wrote:

quoted

This patch introduce the following functions to handle btrfs subpage
uptodate status:
- btrfs_subpage_set_uptodate()
- btrfs_subpage_clear_uptodate()
- btrfs_subpage_test_uptodate()
   Those helpers can only be called when the range is ensured to be
   inside the page.

- btrfs_page_set_uptodate()
- btrfs_page_clear_uptodate()
- btrfs_page_test_uptodate()
   Those helpers can handle both regular sector size and subpage 
without
   problem.
   Although caller should still ensure that the range is inside the 
page.

Signed-off-by: Qu Wenruo <redacted>
---
  fs/btrfs/subpage.h | 115 
+++++++++++++++++++++++++++++++++++++++++++++
  1 file changed, 115 insertions(+)

diff --git a/fs/btrfs/subpage.h b/fs/btrfs/subpage.h
index d8b34879368d..3373ef4ffec1 100644
--- a/fs/btrfs/subpage.h
+++ b/fs/btrfs/subpage.h

@@ -23,6 +23,7 @@

  struct btrfs_subpage {
      /* Common members for both data and metadata pages */
      spinlock_t lock;
+    u16 uptodate_bitmap;
      union {
          /* Structures only used by metadata */
          bool under_alloc;

@@ -78,4 +79,118 @@ static inline void 

btrfs_page_end_meta_alloc(struct btrfs_fs_info *fs_info,
  int btrfs_attach_subpage(struct btrfs_fs_info *fs_info, struct 
page *page);
  void btrfs_detach_subpage(struct btrfs_fs_info *fs_info, struct 
page *page);
+/*
+ * Convert the [start, start + len) range into a u16 bitmap
+ *
+ * E.g. if start == page_offset() + 16K, len = 16K, we get 0x00f0.
+ */
+static inline u16 btrfs_subpage_calc_bitmap(struct btrfs_fs_info 
*fs_info,
+            struct page *page, u64 start, u32 len)
+{
+    int bit_start = offset_in_page(start) >> fs_info->sectorsize_bits;
+    int nbits = len >> fs_info->sectorsize_bits;
+
+    /* Basic checks */
+    ASSERT(PagePrivate(page) && page->private);
+    ASSERT(IS_ALIGNED(start, fs_info->sectorsize) &&
+           IS_ALIGNED(len, fs_info->sectorsize));
+
+    /*
+     * The range check only works for mapped page, we can
+     * still have unampped page like dummy extent buffer pages.
+     */
+    if (page->mapping)
+        ASSERT(page_offset(page) <= start &&
+            start + len <= page_offset(page) + PAGE_SIZE);
+    /*
+     * Here nbits can be 16, thus can go beyond u16 range. Here we 
make the
+     * first left shift to be calculated in unsigned long (u32), then
+     * truncate the result to u16.
+     */
+    return (u16)(((1UL << nbits) - 1) << bit_start);
+}
+
+static inline void btrfs_subpage_set_uptodate(struct btrfs_fs_info 
*fs_info,
+            struct page *page, u64 start, u32 len)
+{
+    struct btrfs_subpage *subpage = (struct btrfs_subpage 
*)page->private;
+    u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len);
+    unsigned long flags;
+
+    spin_lock_irqsave(&subpage->lock, flags);
+    subpage->uptodate_bitmap |= tmp;
+    if (subpage->uptodate_bitmap == U16_MAX)
+        SetPageUptodate(page);
+    spin_unlock_irqrestore(&subpage->lock, flags);
+}
+
+static inline void btrfs_subpage_clear_uptodate(struct 
btrfs_fs_info *fs_info,
+            struct page *page, u64 start, u32 len)
+{
+    struct btrfs_subpage *subpage = (struct btrfs_subpage 
*)page->private;
+    u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len);
+    unsigned long flags;
+
+    spin_lock_irqsave(&subpage->lock, flags);
+    subpage->uptodate_bitmap &= ~tmp;
+    ClearPageUptodate(page);
+    spin_unlock_irqrestore(&subpage->lock, flags);
+}
+
+/*
+ * Unlike set/clear which is dependent on each page status, for 
test all bits
+ * are tested in the same way.
+ */
+#define DECLARE_BTRFS_SUBPAGE_TEST_OP(name)                \
+static inline bool btrfs_subpage_test_##name(struct btrfs_fs_info 
*fs_info, \
+            struct page *page, u64 start, u32 len)        \
+{                                    \
+    struct btrfs_subpage *subpage = (struct btrfs_subpage 
*)page->private; \
+    u16 tmp = btrfs_subpage_calc_bitmap(fs_info, page, start, len); \
+    unsigned long flags;                        \
+    bool ret;                            \
+                                    \
+    spin_lock_irqsave(&subpage->lock, flags);            \
+    ret = ((subpage->name##_bitmap & tmp) == tmp);            \
+    spin_unlock_irqrestore(&subpage->lock, flags);            \
+    return ret;                            \
+}
+DECLARE_BTRFS_SUBPAGE_TEST_OP(uptodate);
+
+/*
+ * Note that, in selftest, especially extent-io-tests, we can have 
empty
+ * fs_info passed in.
+ * Thankfully in selftest, we only test sectorsize == PAGE_SIZE 
cases so far,
+ * thus we can fall back to regular sectorsize branch.
+ */
+#define DECLARE_BTRFS_PAGE_OPS(name, set_page_func, 
clear_page_func,    \
+                   test_page_func)                \
+static inline void btrfs_page_set_##name(struct btrfs_fs_info 
*fs_info,    \
+            struct page *page, u64 start, u32 len)        \
+{                                    \
+    if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE) {    \
+        set_page_func(page);                    \
+        return;                            \
+    }                                \
+    btrfs_subpage_set_##name(fs_info, page, start, len);        \
+}                                    \
+static inline void btrfs_page_clear_##name(struct btrfs_fs_info 
*fs_info, \
+            struct page *page, u64 start, u32 len)        \
+{                                    \
+    if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE) {    \
+        clear_page_func(page);                    \
+        return;                            \
+    }                                \
+    btrfs_subpage_clear_##name(fs_info, page, start, len);        \
+}                                    \
+static inline bool btrfs_page_test_##name(struct btrfs_fs_info 
*fs_info, \
+            struct page *page, u64 start, u32 len)        \
+{                                    \
+    if (unlikely(!fs_info) || fs_info->sectorsize == PAGE_SIZE)    \
+        return test_page_func(page);                \
+    return btrfs_subpage_test_##name(fs_info, page, start, len);    \
+}

Another thing I just realized is you're doing this

btrfs_page_set_uptodate(fs_info, page, eb->start, eb->len);

but we default to a nodesize > PAGE_SIZE on x86.  This is fine, 
because you're checking fs_info->sectorsize == PAGE_SIZE, which will 
mean we do the right thing.

But what happens if fs_info->nodesize < PAGE_SIZE && 
fs_info->sectorsize == PAGE_SIZE?  We by default have fs'es that 
->nodesize != ->sectorsize, so really what we should be doing is 
checking if len == PAGE_SIZE here, but then you need to take into 
account the case that eb->len > PAGE_SIZE.  Fix this to do the right 
thing in either of those cases. Thanks,

Impossible.

Nodesize must be >= sectorsize.

As sectorsize is currently the minimal access unit for both data and 
metadata.

Ok the consider the alternative, we have PAGE_SIZE == 64k, nodesize == 
64k and sectorsize == 4k, something that's actually allowed.  You're now 
doing the subpage operations on something that won't/shouldn't have the 
subpage private attached to the page.  We need to key off of the right 
thing, so for metadata we need to check ->nodesize, and data we check 
->sectorsize, and for these accessors you can simply do len >= 
PAGE_SIZE.  Thanks.

For nodesize == 64K and sectorsize == 4K, subpage way of handling it 
still works.

eb->len == 64K now, btrfs_page_set_uptodate() for subpage will just mark 
the full page uptodate.

I tend not to make the nodesize == 64K a special case, or the check 
condition will be a mess.

Now we unify the check to just sectorsize == PAGE_SIZE, nothing else to 
bother.

Thanks,
Qu

Josef