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

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Message-ID: <aR_ultJzXh1rmOKs@google.com>
Date: Fri, 21 Nov 2025 04:46:14 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Matthew Wilcox <willy@...radead.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 11/21, Matthew Wilcox wrote:
> 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.

So, the sequence that I'd like to optimize is mmap(MAP_POPULATE) followed
by  mlock(). For example, mmap() takes 1 second to load 4GB data, and mlock()
takes 330ms additionally in order to migrate all the pages into inaccessible
map, IIUC.

So, I'm thinking to combine two operations into single fadvise() with whatever
advise. Does it make sense?

> 
> > 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
> >