[2/2] mm: support POSIX_FADV_NOREUSE for generic fadvise handler

Commit Message

Yuanchu Xie Dec. 22, 2022, 6:13 a.m. UTC

From: Yu Zhao <[e-mail]>

POSIX_FADV_NOREUSE allows an application to specify that accesses to
file data does not follow LRU and is used only once. Since 2.6.18 this
is a no-op. We add FMODE_NOREUSE, checked in vma_has_locality to prevent
LRU activation.

Signed-off-by: Yu Zhao <[e-mail]>
Signed-off-by: Yuanchu Xie <[e-mail]>
---
 include/linux/fs.h        | 2 ++
 include/linux/mm_inline.h | 3 +++
 mm/fadvise.c              | 5 ++++-
 3 files changed, 9 insertions(+), 1 deletion(-)

Comments

Yu Zhao Dec. 22, 2022, 9:37 p.m. UTC | #1

On Wed, Dec 21, 2022 at 11:13 PM Yuanchu Xie <[e-mail]> wrote:

Thanks for following up on this.

> POSIX_FADV_NOREUSE allows an application to specify that accesses to
> file data does not follow LRU and is used only once. Since 2.6.18 this
> is a no-op. We add FMODE_NOREUSE, checked in vma_has_locality to prevent
> LRU activation.

This needs to include what you plan to write on the man page.

A few questions to answer:
1. Does this flag work with accesses via FDs?
2. If there is a random or sequential file VMA, should the user choose
this flag or the VMA flag or both? Consider a) how those flags affect
readahead; b) their scopes, i.e., per VMA or per file.

Please also follow up with Jens to add this flag to fio.

Micheal reported that SVT-AV1 regressed with MGLRU, which is the only
real one [1]. The following not only fixes the regression but also
improves the baseline. Please follow up on that as well.

--- a/Source/App/EncApp/EbAppMain.c
+++ b/Source/App/EncApp/EbAppMain.c
@@ -115,6 +115,7 @@ void init_memory_file_map(EbConfig* config) {
             fseeko(config->input_file, curr_loc, SEEK_SET); // seek
back to that location
 #ifndef _WIN32
             config->mmap.fd = fileno(config->input_file);
+            posix_fadvise(config->mmap.fd, 0, 0, POSIX_FADV_NOREUSE);
 #endif
         }
         config->mmap.file_frame_it = 0;

[1] https://openbenchmarking.org/result/2209259-PTS-MGLRU8GB57

Patch

diff --git a/include/linux/fs.h b/include/linux/fs.h
index 066555ad1bf8..5660ed0edf1a 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -166,6 +166,8 @@  typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 /* File supports DIRECT IO */
 #define	FMODE_CAN_ODIRECT	((__force fmode_t)0x400000)
 
+#define	FMODE_NOREUSE		((__force fmode_t)0x800000)
+
 /* File was opened by fanotify and shouldn't generate fanotify events */
 #define FMODE_NONOTIFY		((__force fmode_t)0x4000000)
 
diff --git a/include/linux/mm_inline.h b/include/linux/mm_inline.h
index 80c0f6901ead..024f834d952d 100644
--- a/include/linux/mm_inline.h
+++ b/include/linux/mm_inline.h
@@ -583,6 +583,9 @@  static inline bool vma_has_locality(struct vm_area_struct *vma)
 	if (vma->vm_flags & (VM_SEQ_READ | VM_RAND_READ))
 		return false;
 
+	if (vma->vm_file && (vma->vm_file->f_mode & FMODE_NOREUSE))
+		return false;
+
 	return true;
 }
 
diff --git a/mm/fadvise.c b/mm/fadvise.c
index bf04fec87f35..fb7c5f43fd2a 100644
--- a/mm/fadvise.c
+++ b/mm/fadvise.c
@@ -80,7 +80,7 @@  int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 	case POSIX_FADV_NORMAL:
 		file->f_ra.ra_pages = bdi->ra_pages;
 		spin_lock(&file->f_lock);
-		file->f_mode &= ~FMODE_RANDOM;
+		file->f_mode &= ~(FMODE_RANDOM | FMODE_NOREUSE);
 		spin_unlock(&file->f_lock);
 		break;
 	case POSIX_FADV_RANDOM:
@@ -107,6 +107,9 @@  int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice)
 		force_page_cache_readahead(mapping, file, start_index, nrpages);
 		break;
 	case POSIX_FADV_NOREUSE:
+		spin_lock(&file->f_lock);
+		file->f_mode |= FMODE_NOREUSE;
+		spin_unlock(&file->f_lock);
 		break;
 	case POSIX_FADV_DONTNEED:
 		__filemap_fdatawrite_range(mapping, offset, endbyte,