feat: readahead #1391

xboHodx · 2025-11-20T08:54:58Z

新增log2和ranges工具模块
添加文件预读功能支持

- 添加log2模块实现2的幂次相关计算函数 - 添加ranges模块实现连续整数范围合并功能 - 在mod.rs中导出新增模块

- 新增readahead模块实现文件预读算法 - 修改page_cache模块支持预读标记 - 在File结构体中添加预读状态管理 - 为PageFlags添加PG_READAHEAD标志位

Copilot

Pull Request Overview

This PR implements file readahead functionality for the DragonOS kernel to improve I/O performance by prefetching pages before they are explicitly requested. The implementation includes utility modules for power-of-two operations and range merging, along with an on-demand readahead algorithm.

Key changes:

Adds log2 and ranges utility modules for supporting readahead calculations and optimization
Implements on-demand readahead algorithm in readahead.rs with sync/async readahead entry points
Integrates readahead into file read operations with automatic triggering based on access patterns

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 13 comments.

Show a summary per file

File	Description
`kernel/src/libs/log2.rs`	New utility module providing power-of-two rounding functions for readahead window size calculations
`kernel/src/libs/ranges.rs`	New utility module to merge consecutive page indices into ranges for efficient batch I/O operations
`kernel/src/libs/mod.rs`	Module declarations for the new log2 and ranges utilities
`kernel/src/mm/readahead.rs`	Core readahead implementation with state tracking, control logic, and on-demand algorithm
`kernel/src/mm/page.rs`	Adds `PG_READAHEAD` flag to mark pages that trigger asynchronous readahead
`kernel/src/mm/mod.rs`	Declares readahead module and adds `Sized` trait bounds to read/write methods
`kernel/src/filesystem/vfs/file.rs`	Integrates readahead into file operations, adding state tracking and triggering logic in `do_read`
`kernel/src/filesystem/page_cache.rs`	Refactors `create_pages` to support partial pages and makes it public for readahead use

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

kernel/src/libs/ranges.rs

kernel/src/filesystem/vfs/file.rs

kernel/src/mm/readahead.rs

kernel/src/filesystem/vfs/file.rs

kernel/src/filesystem/page_cache.rs

Copilot · 2025-11-20T09:00:15Z

kernel/src/filesystem/page_cache.rs

+    pub fn create_pages(&mut self, start_page_index: usize, buf: &[u8]) -> Result<(), SystemError> {
+        if buf.is_empty() {
            return Ok(());
        }


[nitpick] The old implementation had an assertion assert!(buf.len().is_multiple_of(MMArch::PAGE_SIZE)) which enforced that the buffer length must be a multiple of page size. The new implementation removes this assertion and handles partial pages. While this is more flexible, if callers were relying on this assertion to catch bugs, they may now silently get unexpected behavior. Consider documenting this behavior change or adding a debug assertion to help catch potential misuse during development.

kernel/src/filesystem/page_cache.rs

- 重构页缓存分配逻辑，改进错误处理时资源释放 - 修正file_readahead函数返回值为Result<(), SystemError> - 更新文档注释中的函数引用名称 - 优化预读控制逻辑，移除不必要的unwrap调用

fslongjin · 2025-11-20T15:39:43Z

kernel/src/filesystem/page_cache.rs

-
-        let len = buf.len();
-        if len == 0 {
+    pub fn create_pages(&mut self, start_page_index: usize, buf: &[u8]) -> Result<(), SystemError> {


为什么不再需要 assert!(buf.len().is_multiple_of(MMArch::PAGE_SIZE));

文件大小不一定是页面大小的整数倍，
let page_len = core::cmp::min(MMArch::PAGE_SIZE, buf.len() - buf_offset);
后面
dst[..page_len].copy_from_slice(&buf[buf_offset..buf_offset + page_len]);
这样写就能保证比如最后一页这种不满一页的数据也能写入到页面中

fslongjin · 2025-11-20T15:41:33Z

kernel/src/filesystem/vfs/file.rs

        self.do_write(offset, len, buf, false)
    }

+    fn file_readahead(&self, offset: usize, len: usize) -> Result<(), SystemError> {


如果该inode的page cache已经存在（比如当前文件已经预读过，或者当前inode对应的其他file已经预读过），那还会预读，创建新的Page cache吗？

page_cache是inode的，预读前先检查页面是否已经存在。逻辑上都是从第一个缺页的地方开始实际的读

fslongjin · 2025-11-20T15:42:07Z

kernel/src/libs/log2.rs

+#[inline]
+pub const fn round_up_pow_of_two(n: usize) -> usize {
+    if n < 2 {
+        return 1;
+    }
+
+    1usize << (usize::BITS - (n - 1).leading_zeros())
+}
+
+#[inline]
+#[allow(unused)]
+pub const fn round_down_pow_of_two(n: usize) -> usize {
+    if n < 2 {
+        return n;
+    }
+
+    1usize << (usize::BITS - (n).leading_zeros() - 1)
+}
+
+/// 检查一个数是否是2的幂次
+#[inline]
+#[allow(unused)]
+pub const fn is_power_of_two(n: usize) -> bool {
+    n > 0 && (n & (n - 1)) == 0
+}


我怎么感觉这些函数的功能rust已经内置了？

确实，我改掉

fslongjin · 2025-11-21T16:50:07Z

测例没过

xboHodx · 2025-11-22T04:03:26Z

测例没过

这是因为在create_pages时设置PG_UPTODATE。应该有才对，但是内核中对这个标志的处理不足，导致panic。我先改掉，现在提个issue

fslongjin

测例没过。本地运行make test-syscall看看

xboHodx · 2025-11-25T09:43:55Z

测例没过。本地运行make test-syscall看看

本地跑make test-syscall没问题，单独跑duptest就会报错，在最新主线上跑也是如此。

fslongjin · 2025-11-25T16:39:17Z

本地跑make test-syscall没问题，单独跑duptest就会报错，在最新主线上跑也是如此。

这个pr肯定是有问题的，因为主线的是能通过的。并且你的分支跟主线之间有差异，先同步一下再跑看看？

xboHodx added 8 commits November 18, 2025 22:33

feat(libs): 新增log2和ranges工具模块

62bfb06

- 添加log2模块实现2的幂次相关计算函数 - 添加ranges模块实现连续整数范围合并功能 - 在mod.rs中导出新增模块

feat(filesystem): 添加文件预读功能支持

2ea3104

- 新增readahead模块实现文件预读算法 - 修改page_cache模块支持预读标记 - 在File结构体中添加预读状态管理 - 为PageFlags添加PG_READAHEAD标志位

fix(readahead): 将do_read中的预读逻辑单独作为一个函数

bd64e3f

feat(readahead): 交换判断顺续读顺序

2290c8b

减少一次加锁

1a26831

将readahead.rs移动到mm下面

45a0656

Merge branch 'master' of github.com:xboHodx/DragonOS into feat/readahead

df996e0

fmt

0e30c8d

Copilot AI review requested due to automatic review settings November 20, 2025 08:54

github-actions bot added the ambiguous The title of PR/issue doesn't match the format label Nov 20, 2025

Copilot started reviewing on behalf of xboHodx November 20, 2025 08:55 View session

Copilot finished reviewing on behalf of xboHodx November 20, 2025 08:57

Copilot AI reviewed Nov 20, 2025

View reviewed changes

xboHodx closed this Nov 20, 2025

取消注释

d65805c

xboHodx reopened this Nov 20, 2025

xboHodx added 2 commits November 20, 2025 19:26

删去日志

0463f1a

删去日志

db1f01b

sparkzky changed the title ~~Feat/readahead~~ feat: readahead Nov 20, 2025

github-actions bot added enhancement New feature or request and removed ambiguous The title of PR/issue doesn't match the format labels Nov 20, 2025

fslongjin reviewed Nov 20, 2025

View reviewed changes

删去重复的函数

527a7db

xboHodx added 3 commits November 22, 2025 10:18

Merge branch 'master' of github.com:xboHodx/DragonOS into feat/readahead

26ab3f6

fmt

8036fd5

暂时去掉在create_pages时设置PG_UPTODATE

cc3ce28

fslongjin mentioned this pull request Nov 24, 2025

缺少对于PG_UPTODATE标志的处理 #1401

Open

fslongjin approved these changes Nov 24, 2025

View reviewed changes

fslongjin requested changes Nov 24, 2025

View reviewed changes

Merge branch 'master' of github.com:xboHodx/DragonOS into feat/readahead

ea45355

fslongjin approved these changes Nov 26, 2025

View reviewed changes

fslongjin merged commit 53df56c into DragonOS-Community:master Nov 26, 2025
11 checks passed

Uh oh!

feat: readahead #1391

feat: readahead #1391

Uh oh!

Conversation

xboHodx commented Nov 20, 2025

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull Request Overview

Reviewed Changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Copilot AI Nov 20, 2025

Choose a reason for hiding this comment

Uh oh!

Uh oh!

fslongjin Nov 20, 2025

Choose a reason for hiding this comment

Uh oh!

xboHodx Nov 21, 2025

Choose a reason for hiding this comment

Uh oh!

fslongjin Nov 20, 2025

Choose a reason for hiding this comment

Uh oh!

xboHodx Nov 21, 2025

Choose a reason for hiding this comment

Uh oh!

fslongjin Nov 20, 2025

Choose a reason for hiding this comment

Uh oh!

xboHodx Nov 21, 2025

Choose a reason for hiding this comment

Uh oh!

fslongjin commented Nov 21, 2025

Uh oh!

xboHodx commented Nov 22, 2025

Uh oh!

fslongjin left a comment

Choose a reason for hiding this comment

Uh oh!

xboHodx commented Nov 25, 2025

Uh oh!

fslongjin commented Nov 25, 2025

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

2 participants