Messages in this thread | | | Subject | Re: [PATCH] readahead: Update the file_ra_state.ra_pages with each readahead operation | From | Youling Tang <> | Date | Tue, 31 Oct 2023 09:56:29 +0800 |
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Hi, Matthew
On 2023/10/31 上午12:47, Matthew Wilcox wrote: > On Mon, Oct 30, 2023 at 03:41:30PM +0800, Youling Tang wrote: >> From: Youling Tang <tangyouling@kylinos.cn> >> >> Changing the read_ahead_kb value midway through a sequential read of a >> large file found that the ra->ra_pages value remained unchanged (new >> ra_pages can only be detected the next time the file is opened). Because >> file_ra_state_init() is only called once in do_dentry_open() in most >> cases. >> >> In ondemand_readahead(), update bdi->ra_pages to ra->ra_pages to ensure >> that the maximum pages that can be allocated by the readahead algorithm >> are the same as (read_ahead_kb * 1024) / PAGE_SIZE after read_ahead_kb >> is modified. > Explain to me why this is the correct behaviour. Because I initially expected to immediately improve the current read performance by modifying read_ahead_kb when reading large files sequentially. > Many things are only initialised at open() time and are not updated until > the next open(). This is longstanding behaviour that some apps expect. Thanks for your explanation. I will discard this change if the next open update is in line with the apps expectation.
Thanks, Youling.
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