linux-kernel - Re: [PATCH] [RFC] mm/fadvise: introduce POSIX_FADV

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Message-ID: <aR_pCGtcc7ASeA77@casper.infradead.org>
Date: Fri, 21 Nov 2025 04:22:32 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
	Christian Brauner <brauner@...nel.org>
Subject: Re: [PATCH] [RFC] mm/fadvise: introduce POSIX_FADV_MLOCK

On Fri, Nov 21, 2025 at 03:27:18AM +0000, Jaegeuk Kim wrote:
> This patch introduces a new POSIX_FADV_MLOCK which 1) invalidates the range of
> cached pages, 2) sets the mapping as inaccessible, 3) POSIX_FADV_WILLNEED loads
> pages directly to the inaccessible mapping.

... what?

This seems like something which is completely different from mlock().
So it needs a different name.

But I don't understand the point of this, whatever it's called.  Need
more information.

> The inaccessible pages will be invalidated by evict_inode or explicit munlock().
> 
> Cc: Matthew Wilcox (Oracle) <willy@...radead.org>
> Cc: Christian Brauner <brauner@...nel.org>
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  include/uapi/linux/fadvise.h |  2 ++
>  mm/fadvise.c                 | 14 ++++++++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/include/uapi/linux/fadvise.h b/include/uapi/linux/fadvise.h
> index 0862b87434c2..06018688b99b 100644
> --- a/include/uapi/linux/fadvise.h
> +++ b/include/uapi/linux/fadvise.h
> @@ -19,4 +19,6 @@
>  #define POSIX_FADV_NOREUSE	5 /* Data will be accessed once.  */
>  #endif
>  
> +#define POSIX_FADV_MLOCK	8 /* Load pages into inaccessible map.  */
> +
>  #endif	/* FADVISE_H_INCLUDED */
> diff --git a/mm/fadvise.c b/mm/fadvise.c
> index 588fe76c5a14..849b151d2024 100644
> --- a/mm/fadvise.c
> +++ b/mm/fadvise.c
> @@ -56,6 +56,7 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
>  		case POSIX_FADV_WILLNEED:
>  		case POSIX_FADV_NOREUSE:
>  		case POSIX_FADV_DONTNEED:
> +		case POSIX_FADV_MLOCK:
>  			/* no bad return value, but ignore advice */
>  			break;
>  		default:
> @@ -93,6 +94,19 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
>  		file->f_mode &= ~FMODE_RANDOM;
>  		spin_unlock(&file->f_lock);
>  		break;
> +	case POSIX_FADV_MLOCK:
> +		/* Remove the cached pages. */
> +		if (!mapping_unevictable(mapping)) {
> +			invalidate_inode_pages2_range(mapping,
> +					offset >> PAGE_SHIFT,
> +					(offset + len - 1) >> PAGE_SHIFT);
> +
> +			/* set the mapping is unevictable */
> +			filemap_invalidate_lock(mapping);
> +			mapping_set_inaccessible(mapping);
> +			filemap_invalidate_unlock(mapping);
> +		}
> +		fallthrough;
>  	case POSIX_FADV_WILLNEED:
>  		/* First and last PARTIAL page! */
>  		start_index = offset >> PAGE_SHIFT;
> -- 
> 2.52.0.487.g5c8c507ade-goog
>