Re: [RFC PATCH] mm: Add large folio support for async readahead

[Matthew Wilcox <willy@infradead.org>]

On Tue, Nov 05, 2024 at 11:01:01AM +0800, Yafang Shao wrote:
> Upon further analysis, it appears that the behavior depends on the
> /sys/block/*/queue/read_ahead_kb setting. On my test server, this
> parameter is set to 128KB. For the current approach to work without
> modification, it would need to be 2MB-aligned.
> 
> However, I believe MADV_HUGEPAGE behavior should not be dependent on
> the value of read_ahead_kb. It would be more robust if the kernel
> automatically aligned it to 2MB when MADV_HUGEPAGE is enabled. The
> following changes ensure compatibility with non-2MB-aligned
> read_ahead_kb values:

or maybe:

static unsigned long get_next_ra_size(struct file_ra_state *ra,
                                      unsigned long max)
{
        unsigned long cur = ra->size;

        if (cur < max / 16)
                return 4 * cur;
        if (cur <= max / 2)
                return 2 * cur;
+	if (cur > max)
+		return cur;
        return max;
}