linux-kernel - Re: [f2fs-dev] [PATCH 1/4] mm/readahead: fix the broken readahead for POSIX_FADV

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Message-ID: <3420618e-a108-4d29-b941-e94d3e9bb55e@kernel.org>
Date: Mon, 1 Dec 2025 12:40:08 -0800
From: Chao Yu <chao@...nel.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>, linux-kernel@...r.kernel.org,
 linux-f2fs-devel@...ts.sourceforge.net
Cc: chao@...nel.org
Subject: Re: [f2fs-dev] [PATCH 1/4] mm/readahead: fix the broken readahead for
 POSIX_FADV_WILLNEED

On 2025/12/2 03:16, Jaegeuk Kim via Linux-f2fs-devel wrote:
> This patch fixes the broken readahead flow for POSIX_FADV_WILLNEED, where
> the problem is, in force_page_cache_ra(nr_to_read), nr_to_read is cut by
> the below code.
> 
>       max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);
>       nr_to_read = min_t(unsigned long, nr_to_read, max_pages);
> 
> IOWs, we are not able to read ahead larger than the above max_pages which
> is most likely the range of 2MB and 16MB. Note, it doesn't make sense
> to set ra->ra_pages to the entire file size. Instead, let's fix this logic.
> 
> Before:
> f2fs_fadvise: dev = (252,16), ino = 14, i_size = 4294967296 offset:0, len:4294967296, advise:3
> page_cache_ra_unbounded: dev=252:16 ino=e index=0 nr_to_read=512 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=512 nr_to_read=512 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=1024 nr_to_read=512 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=1536 nr_to_read=512 lookahead_size=0
> 
> After:
> f2fs_fadvise: dev = (252,16), ino = 14, i_size = 4294967296 offset:0, len:4294967296, advise:3
> page_cache_ra_unbounded: dev=252:16 ino=e index=0 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=2048 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=4096 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=6144 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=8192 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=10240 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=12288 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=14336 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=16384 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=18432 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=20480 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=22528 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=24576 nr_to_read=2048 lookahead_size=0
> ...
> page_cache_ra_unbounded: dev=252:16 ino=e index=1042432 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=1044480 nr_to_read=2048 lookahead_size=0
> page_cache_ra_unbounded: dev=252:16 ino=e index=1046528 nr_to_read=2048 lookahead_size=0
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>

Reviewed-by: Chao Yu <chao@...nel.org>

Thanks,