[Deepin-Kernel-SIG] [linux 6.6-y] [Upstream] Add folio_end_read

[opsiff]

The core of this patchset is the new folio_end_read() call which
filesystems can use when finishing a page cache read instead of separate
calls to mark the folio uptodate and unlock it. As an illustration of
its use, I converted ext4, iomap & mpage; more can be converted.

I think that's useful by itself, but the interesting optimisation is
that we can implement that with a single XOR instruction that sets the
uptodate bit, clears the lock bit, tests the waiter bit and provides a
write memory barrier. That removes one memory barrier and one atomic
instruction from each page read, which seems worth doing. That's in
patch 15.

The last two patches could be a separate series, but basically we can do
the same thing with the writeback flag that we do with the unlock flag;
clear it and test the waiters bit at the same time.

v2:

• Update to 6.6-rc4
• Simplify iomap's use of folio_end_read() as suggested by Linus
• Fix weird Alpha assembly, as suggested by Linus
• Implement xor_unlock_is_negative_byte for Coldfire
• Add a likely() to folio_end_read() after studying the Coldfire assembly

Matthew Wilcox (Oracle) (17):
iomap: Hold state_lock over call to ifs_set_range_uptodate()
iomap: Protect read_bytes_pending with the state_lock
mm: Add folio_end_read()
ext4: Use folio_end_read()
buffer: Use folio_end_read()
iomap: Use folio_end_read()
bitops: Add xor_unlock_is_negative_byte()
alpha: Implement xor_unlock_is_negative_byte
m68k: Implement xor_unlock_is_negative_byte
mips: Implement xor_unlock_is_negative_byte
powerpc: Implement arch_xor_unlock_is_negative_byte on 32-bit
riscv: Implement xor_unlock_is_negative_byte
s390: Implement arch_xor_unlock_is_negative_byte
mm: Delete checks for xor_unlock_is_negative_byte()
mm: Add folio_xor_flags_has_waiters()
mm: Make __end_folio_writeback() return void
mm: Use folio_xor_flags_has_waiters() in folio_end_writeback()

Summary by Sourcery

Introduce folio_end_read() to simplify and optimize page cache read completion. This new function combines setting the uptodate bit, clearing the lock bit, and testing the waiter bit into a single operation, reducing memory barriers and atomic instructions. It also updates writeback flag handling.

New Features:

• Introduce folio_end_read() to streamline page cache read completion.
• Introduce folio_xor_flags_has_waiters() to change some folio flags and check for waiters

[sourcery-ai]

Reviewer's Guide by Sourcery

This pull request introduces folio_end_read() to simplify page cache read completion, optimizes folio_end_writeback(), updates iomap to use spinlocks, and adds xor_unlock_is_negative_byte() for atomic XOR operations.

Sequence diagram for folio_end_read()

sequenceDiagram
    participant FS as FileSystem
    participant FM as Filemap

    FS->>FM: folio_end_read(folio, success)
    alt success is true
        FM->>FM: mask |= PG_uptodate
    end
    FM->>FM: folio_xor_flags_has_waiters(folio, mask)
    alt waiters exist
        FM->>FM: folio_wake_bit(folio, PG_locked)
    end

Loading

Sequence diagram for iomap_finish_folio_read()

sequenceDiagram
    participant IOM as iomap
    participant FM as Filemap

    IOM->>IOM: spin_lock_irqsave(&ifs->state_lock, flags)
    alt !error
        IOM->>IOM: uptodate = ifs_set_range_uptodate(folio, ifs, off, len)
    end
    IOM->>IOM: ifs->read_bytes_pending -= len
    IOM->>IOM: finished = !ifs->read_bytes_pending
    IOM->>IOM: spin_unlock_irqrestore(&ifs->state_lock, flags)
    alt error
        IOM->>FM: folio_set_error(folio)
    end
    alt finished
        IOM->>FM: folio_end_read(folio, uptodate)
    end

Loading

Updated class diagram for iomap_folio_state

classDiagram
    class iomap_folio_state {
        -spinlock_t state_lock
        -unsigned int read_bytes_pending
        -atomic_t write_bytes_pending
        -unsigned long state
    }
    note for iomap_folio_state "read_bytes_pending changed from atomic_t to unsigned int and is now protected by a spinlock"

Loading

File-Level Changes

Change	Details	Files
Introduces folio_end_read() to streamline page cache read completion, replacing separate folio_mark_uptodate() and folio_unlock() calls with a single function.	Adds folio_end_read() function. Updates filesystems (ext4, iomap, buffer) to use folio_end_read(). Optimizes by using a single XOR instruction to set the uptodate bit, clear the lock bit, and test the waiter bit, reducing memory barriers and atomic instructions. Adds folio_xor_flags_has_waiters() to check for waiters during flag manipulation.	mm/filemap.c fs/iomap/buffered-io.c mm/page-writeback.c include/asm-generic/bitops/instrumented-lock.h arch/mips/include/asm/bitops.h arch/m68k/include/asm/bitops.h arch/powerpc/include/asm/bitops.h arch/alpha/include/asm/bitops.h include/asm-generic/bitops/lock.h include/linux/page-flags.h fs/buffer.c arch/mips/lib/bitops.c fs/ext4/readpage.c arch/riscv/include/asm/bitops.h arch/x86/include/asm/bitops.h arch/s390/include/asm/bitops.h kernel/kcsan/kcsan_test.c kernel/kcsan/selftest.c mm/kasan/kasan_test.c include/linux/pagemap.h
Optimizes folio_end_writeback() by using folio_xor_flags_has_waiters() to clear the writeback flag and test for waiters simultaneously.	Modifies folio_end_writeback() to use folio_xor_flags_has_waiters(). Removes folio_test_clear_writeback() call. Makes __end_folio_writeback() return void and return a boolean indicating whether there are waiters.	mm/filemap.c mm/page-writeback.c
Updates iomap to use spinlocks to protect read_bytes_pending and state bitmap.	Replaces atomic_t for read_bytes_pending with an unsigned int protected by a spinlock. Holds state_lock over call to ifs_set_range_uptodate(). Modifies ifs_set_range_uptodate to return a boolean indicating whether the folio is fully uptodate.	fs/iomap/buffered-io.c
Introduces xor_unlock_is_negative_byte() and architecture-specific implementations for atomic XOR and negative byte test.	Adds xor_unlock_is_negative_byte() function. Implements xor_unlock_is_negative_byte for alpha, m68k, mips, powerpc, riscv, and s390 architectures. Removes clear_bit_unlock_is_negative_byte.	bitops: Add xor_unlock_is_negative_byte() alpha: Implement xor_unlock_is_negative_byte m68k: Implement xor_unlock_is_negative_byte mips: Implement xor_unlock_is_negative_byte powerpc: Implement arch_xor_unlock_is_negative_byte on 32-bit riscv: Implement xor_unlock_is_negative_byte s390: Implement arch_xor_unlock_is_negative_byte mm: Delete checks for xor_unlock_is_negative_byte() include/asm-generic/bitops/instrumented-lock.h arch/mips/include/asm/bitops.h arch/m68k/include/asm/bitops.h arch/powerpc/include/asm/bitops.h arch/alpha/include/asm/bitops.h include/asm-generic/bitops/lock.h arch/riscv/include/asm/bitops.h arch/x86/include/asm/bitops.h arch/s390/include/asm/bitops.h arch/mips/lib/bitops.c

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[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please ask for approval from opsiff. For more information see the Code Review Process.

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[sourcery-ai]

Hey @opsiff - I've reviewed your changes - here's some feedback:

Overall Comments:

• The removal of folio_wake seems like it might be premature - is it really unused?
• It looks like you're converting ifs->read_bytes_pending from an atomic to a regular integer, but still using a spinlock - is there a reason it can't be a regular integer without a spinlock?

Here's what I looked at during the review

• 🟢 General issues: all looks good
• 🟢 Security: all looks good
• 🟢 Testing: all looks good
• 🟡 Complexity: 2 issues found
• 🟢 Documentation: all looks good

---

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[sourcery-ai]

issue (complexity): Consider factoring out the conditional and inline assembly duplication into a helper function to improve code reuse and readability.

Consider factoring out the conditional and inline assembly duplication into a helper that picks the “mask” at a single point. For example:

```c
static inline unsigned long xor_unlock_atomic(volatile unsigned long *p,
                                              unsigned long effective_mask)
{
    unsigned long orig;
    if (!kernel_uses_llsc)
        orig = __mips_xor_is_negative_byte(effective_mask, p);
    else
        orig = __test_bit_op(*p, "%0", "xor\t%1, %0, %3", "ir"(effective_mask));
    return orig;
}

static inline bool xor_unlock_is_negative_byte(unsigned long mask,
                                                 volatile unsigned long *p)
{
    unsigned long eff_mask = kernel_uses_llsc ? BIT(7) : mask;
    unsigned long orig;

    smp_mb__before_atomic();
    orig = xor_unlock_atomic(p, eff_mask);
    smp_llsc_mb();

    return (orig & eff_mask) != 0;
}

This consolidates the conditional logic and reduces duplicate inline assembly while retaining original functionality.

[sourcery-ai]

issue (complexity): Consider using GNU atomic builtins to replace the inline assembly loop with a single atomic XOR operation, if the platform supports it, to reduce complexity and duplicate logic while preserving functionality .

Consider using the GNU atomic builtins to simplify the inline assembly loop. For example, if the platform supports __atomic builtins, you can replace the inline assembly with a single atomic XOR operation:

static inline bool xor_unlock_is_negative_byte(unsigned long mask,
                                                 volatile unsigned long *p)
{
    unsigned long old = __atomic_fetch_xor(p, mask, __ATOMIC_ACQ_REL);
    return (old & BIT(7)) != 0;
}

This preserves the functionality while reducing the low-level complexity and duplicate logic.

[deepin-ci-robot]

deepin pr auto review

代码审查意见：

1. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

2. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

3. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

4. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

5. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

6. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

7. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

8. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

9. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

10. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

11. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

12. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

13. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

14. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

15. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

16. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

17. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

18. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

19. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

20. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

21. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

22. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

23. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

24. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

25. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

26. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

27. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

28. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

29. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

30. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

31. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

32. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

33. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

34. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

35. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

36. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

37. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

38. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

39. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

40. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

41. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

42. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

43. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

44. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

45. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

46. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

47. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

48. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

49. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

50. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

51. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

52. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

53. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

54. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

55. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

56. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

57. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这会导致mask的值是128，这可能会影响函数的行为。建议检查PG_locked的值是否正确。

58. 在folio_end_read函数中，folio_xor_flags_has_waiters函数的参数mask被设置为1 << PG_locked，但是PG_locked的值是7，这