Re: [PATCH v5 00/16] mm/rmap: index MAP_PRIVATE file-backed folios by anonymous pgoff

[Matthew Brost <matthew.brost@intel.com>]

On Fri, Aug 14, 2026 at 10:01:19AM +0100, Lorenzo Stoakes (ARM) wrote:
> On Thu, Aug 13, 2026 at 11:53:46AM -0700, Andrew Morton wrote:
> > You'll be mortified to hear that Sashiko wasn't able to find anything
> > to which to apply this.
> 
> :))
> 
> Well, when it's right it's useful, when it's wrong or suggesting unrelated
> what-nots it's less useful :>)
> 

Questioning your assumptions is useful, even when they turn out to be wrong.
Show more lines

> I do locally put things through claude + Chris Mason's prompts a lot, I
> don't always invoke local sashiko as it's very slow and token-heavy or has
> been so far, but am planning to do that more also in future.
> 

Yes, it's kind of odd that Sashiko burns more tokens than a full day of
breakfast, lunch, and dinner service. Running Sashiko is a bottleneck in
my workflow, so I'll defer to others on this list.

> >
> > Sashiko can be guided with a base-commit: tag but I'm not sure how to
> > tell it what tree/branch to try, or even if that's necessary.  Perhaps
> > someone can figure this out sometime.
> 
> b4 gives a base commit, but I think because the trees are rebased it ends
> up being the incorrect one.
> 
> Not sure what the solution is!
> 

We have seen this on the Xe list (our list is based on drm-tip),
typically with cross-subsystem patches. Some cross-subsystem patches
apply and run correctly, while others do not but public CI flows run
based on drm-tip. I do not have a bisect or a clear understanding of
what works and what doesn't, but I think it would be very useful if the
community could better understand the root cause.

Matt

> >
> > maybe
> >
> > hp2:/usr/src/linux-next> git log --oneline | grep "mm/vma: introduce VMA anon page offset field and add helpers"
> > 249646a587dc mm/vma: introduce VMA anon page offset field and add helpers
> >
> > base-commit: 249646a587dc^
> >
> > But that requires that Sashiko be able to poke around in linux-next
> > from previous days.
> >
> > > v5:
> > > * Accumulated tags (thanks everybody!)
> > > * Removed the final 4 patches to be handled later as there are nuances with
> > >   the /dev/zero stuff we need to figure out, as discussed with David.
> > > * Updated the cover letter to reflect this.
> > > * Added comments to vma_flags_is_cow_mapping(),
> > >   vma_[desc_]is_cow_mapping() as per Suren.
> > > * Correct typo as per Suren.
> > > * Reworded test comment in patch 16 from 'fault in' to 'trigger a CoW
> > >   fault' as per David.
> > > * Fix -> 75 char limit in patch 12's commit msg.
> >
> > Here's how v5 altered mm.git.  It's rather substantial, but mainly
> > selftests:
> 
> Thanks for the diff, always useful!
> 
> The noise it's mostly because of dropping the final 4 commits, and as you
> say mostly test stuff that will be sent with whichever approach we decide
> on for MAP_PRIVATE-/dev/zero in the next cycle.
> 
> The actual changes elsewhere are rather trivial otherwise.
> 
> What remains, targeting 2nd week of the merge window, is heavily tested +
> fully reviewed, so all is still very sane :)
> 
> >
> >
> >  drivers/char/mem.c                                     |    8
> >  include/linux/mm.h                                     |   18 -
> >  include/linux/pagemap.h                                |    3
> >  mm/internal.h                                          |   17 -
> >  mm/vma.c                                               |   52 ----
> >  mm/vma.h                                               |    3
> >  mm/vma_internal.h                                      |    1
> >  tools/testing/selftests/mm/merge.c                     |  106 ----------
> >  tools/testing/selftests/proc/proc-self-map-files-001.c |    2
> >  tools/testing/selftests/proc/proc-self-map-files-002.c |    2
> >  tools/testing/vma/include/dup.h                        |   40 ---
> >  tools/testing/vma/tests/mmap.c                         |   50 ----
> >  12 files changed, 40 insertions(+), 262 deletions(-)
> >
> > --- a/drivers/char/mem.c~b
> > +++ a/drivers/char/mem.c
> > @@ -506,7 +506,11 @@ static int mmap_zero_prepare(struct vm_a
> >  	if (vma_desc_test(desc, VMA_SHARED_BIT))
> >  		return shmem_zero_setup_desc(desc);
> >
> > -	/* MAP_PRIVATE semantics are taken care for us by core mm. */
> > +	/*
> > +	 * This is a highly unique situation where we mark a MAP_PRIVATE mapping
> > +	 * of /dev/zero anonymous, despite it not being.
> > +	 */
> > +	vma_desc_set_anonymous(desc);
> >  	return 0;
> >  }
> >
> > @@ -694,7 +698,7 @@ static const struct memdev {
> >  #ifdef CONFIG_DEVPORT
> >  	[4] = { "port", &port_fops, 0, 0 },
> >  #endif
> > -	[DEVZERO_MINOR] = { "zero", &zero_fops, FMODE_NOWAIT, 0666 },
> > +	[5] = { "zero", &zero_fops, FMODE_NOWAIT, 0666 },
> >  	[7] = { "full", &full_fops, 0, 0666 },
> >  	[8] = { "random", &random_fops, FMODE_NOWAIT, 0666 },
> >  	[9] = { "urandom", &urandom_fops, FMODE_NOWAIT, 0666 },
> > --- a/include/linux/mm.h~b
> > +++ a/include/linux/mm.h
> > @@ -740,9 +740,6 @@ static inline bool fault_flag_allow_retr
> >  	{ FAULT_FLAG_INTERRUPTIBLE,	"INTERRUPTIBLE" }, \
> >  	{ FAULT_FLAG_VMA_LOCK,		"VMA_LOCK" }
> >
> > -/* /dev/zero minor device number. Special due to MAP_PRIVATE semantics. */
> > -#define DEVZERO_MINOR	5
> > -
> >  /*
> >   * vm_fault is filled by the pagefault handler and passed to the vma's
> >   * ->fault function. The vma's ->fault is responsible for returning a bitmask
> > @@ -1554,6 +1551,11 @@ static inline void vma_set_anonymous(str
> >  	vma->vm_ops = NULL;
> >  }
> >
> > +static inline void vma_desc_set_anonymous(struct vm_area_desc *desc)
> > +{
> > +	desc->vm_ops = NULL;
> > +}
> > +
> >  static inline bool vma_is_anonymous(const struct vm_area_struct *vma)
> >  {
> >  	return !vma->vm_ops;
> > @@ -2279,8 +2281,7 @@ void unpin_folios(struct folio **folios,
> >   * All mappings backed by anonymous folios (all anonymous mappings and most
> >   * MAP_PRIVATE-file backed ranges) are CoW mappings.
> >   *
> > - * All other mappings (including all writable MAP_SHARED mappings) are
> > - * non-CoW.
> > + * All other mappings (including all MAP_SHARED mappings) are non-CoW.
> >   *
> >   * The criteria are !VMA_SHARED_BIT, VMA_MAYWRITE_BIT.
> >   *
> > @@ -2317,7 +2318,7 @@ static inline bool vma_flags_is_cow_mapp
> >
> >  /**
> >   * vma_is_cow_mapping() - Is this VMA a CoW mapping?
> > - * @vma: The VMA to check.
> > + * @desc: The VMA to check.
> >   *
> >   * See vma_flags_is_cow_mapping() for details.
> >   *
> > @@ -4407,8 +4408,9 @@ static inline unsigned long vma_pages(co
> >   * If @vma is a MAP_PRIVATE file-backed mapping, then this returns the
> >   * page offset within the file.
> >   *
> > - * Edge cases: nommu does not abide by these and CoW MAP_PRIVATE-pfnmap regions
> > - * have their page offset set to the first PFN in the range.
> > + * Edge cases: nommu does not abide by these, MAP_PRIVATE-/dev/zero satisfies
> > + * vma_is_anonymous() but has file-backed page offset, and MAP_PRIVATE-pfnmap
> > + * regions have their page offset set to the first PFN in the range.
> >   *
> >   * Returns: The page offset of the start of @vma.
> >   */
> > --- a/include/linux/pagemap.h~b
> > +++ a/include/linux/pagemap.h
> > @@ -1128,7 +1128,8 @@ static inline pgoff_t linear_anon_page_i
> >  	const pgoff_t pgoff = __linear_anon_page_index(vma, address);
> >
> >  	VM_WARN_ON_ONCE(!vma_is_cow_mapping(vma));
> > -	if (vma_is_anonymous(vma))
> > +	/* Account for MAP_PRIVATE-/dev/zero which is only semi-anonymous. */
> > +	if (vma_is_anonymous(vma) && !vma->vm_file)
> >  		VM_WARN_ON_ONCE(pgoff != linear_page_index(vma, address));
> >
> >  	return pgoff;
> > --- a/mm/internal.h~b
> > +++ a/mm/internal.h
> > @@ -240,18 +240,15 @@ static inline int mmap_file(struct file
> >  {
> >  	int err = vfs_mmap(file, vma);
> >
> > +	if (likely(!err))
> > +		return 0;
> > +
> >  	/*
> > -	 * Either we tried to call the file hook for mmap() and an error arose
> > -	 * or a driver set vma->vm_ops = NULL intending there to be no VMA
> > -	 * operations.
> > -	 *
> > -	 * In the former case the VMA is in an inconsistent state and we mustn't
> > -	 * invoke any further hooks on it, in the latter case the hook actually
> > -	 * wanted no further hooks to be invoked, so fix both by setting dummy
> > -	 * VMA ops.
> > +	 * OK, we tried to call the file hook for mmap(), but an error
> > +	 * arose. The mapping is in an inconsistent state and we must not invoke
> > +	 * any further hooks on it.
> >  	 */
> > -	if (unlikely(err || !vma->vm_ops))
> > -		vma->vm_ops = &vma_dummy_vm_ops;
> > +	vma->vm_ops = &vma_dummy_vm_ops;
> >
> >  	return err;
> >  }
> > --- a/mm/vma.c~b
> > +++ a/mm/vma.c
> > @@ -2621,36 +2621,6 @@ static int __mmap_new_file_vma(struct mm
> >  	return 0;
> >  }
> >
> > -static bool map_is_dev_zero(const struct mmap_state *map)
> > -{
> > -	const struct file *file = map->file;
> > -	struct inode *inode;
> > -
> > -	if (!file)
> > -		return false;
> > -	inode = file_inode(file);
> > -	if (!S_ISCHR(inode->i_mode))
> > -		return false;
> > -	return imajor(inode) == MEM_MAJOR && iminor(inode) == DEVZERO_MINOR;
> > -}
> > -
> > -static void map_set_anon(struct mmap_state *map)
> > -{
> > -	map->file = NULL;
> > -	map->vm_ops = NULL;
> > -	map->pgoff = map->addr >> PAGE_SHIFT;
> > -}
> > -
> > -static bool map_is_private(const struct mmap_state *map)
> > -{
> > -	return !vma_flags_test(&map->vma_flags, VMA_SHARED_BIT);
> > -}
> > -
> > -static bool map_is_anon(const struct mmap_state *map)
> > -{
> > -	return map_is_private(map) && !map->file;
> > -}
> > -
> >  /*
> >   * __mmap_new_vma() - Allocate a new VMA for the region, as merging was not
> >   * possible.
> > @@ -2664,7 +2634,8 @@ static bool map_is_anon(const struct mma
> >  static int __mmap_new_vma(struct mmap_state *map, struct vm_area_struct **vmap,
> >  	struct mmap_action *action)
> >  {
> > -	const bool is_anon = map_is_anon(map);
> > +	const bool is_anon = !map->file &&
> > +		!vma_flags_test(&map->vma_flags, VMA_SHARED_BIT);
> >  	struct vma_iterator *vmi = map->vmi;
> >  	int error = 0;
> >  	struct vm_area_struct *vma;
> > @@ -2806,10 +2777,6 @@ static int call_mmap_prepare(struct mmap
> >  	if (err)
> >  		return err;
> >
> > -	/* Hooks cannot mark themselves anonymous. */
> > -	if (!desc->vm_ops)
> > -		return -EINVAL;
> > -
> >  	err = call_action_prepare(map, desc);
> >  	if (err)
> >  		return err;
> > @@ -2826,21 +2793,16 @@ static int call_mmap_prepare(struct mmap
> >  	map->vm_ops = desc->vm_ops;
> >  	map->vm_private_data = desc->private_data;
> >
> > -	/*
> > -	 * MAP_PRIVATE-/dev/zero mappings are an ancient way of getting
> > -	 * anonymous mappings. Rather than allowing these mappings to be odd
> > -	 * outliers, simply make them truly anonymous.
> > -	 */
> > -	if (map_is_private(map) && map_is_dev_zero(map))
> > -		map_set_anon(map);
> > -
> >  	return 0;
> >  }
> >
> >  static void set_vma_user_defined_fields(struct vm_area_struct *vma,
> >  		struct mmap_state *map)
> >  {
> > -	vma->vm_ops = map->vm_ops;
> > +	if (map->vm_ops)
> > +		vma->vm_ops = map->vm_ops;
> > +	else	/* Only /dev/zero should do this. */
> > +		vma_set_anonymous(vma);
> >  	vma->vm_private_data = map->vm_private_data;
> >  }
> >
> > @@ -2920,7 +2882,7 @@ static unsigned long __mmap_region(struc
> >  		allocated_new = true;
> >  	}
> >
> > -	if (have_mmap_prepare && !map_is_anon(&map))
> > +	if (have_mmap_prepare)
> >  		set_vma_user_defined_fields(vma, &map);
> >
> >  	__mmap_complete(&map, vma);
> > --- a/mm/vma.h~b
> > +++ a/mm/vma.h
> > @@ -267,6 +267,9 @@ static inline void assert_sane_pgoff(str
> >  	 */
> >  	if (!vma_is_anonymous(vma))
> >  		return;
> > +	/* MAP_PRIVATE-/dev/zero is anon, non-NULL vm_file, but has file pgoff. */
> > +	if (vma->vm_file)
> > +		return;
> >  	/* If faulted in, could have been remapped. */
> >  	if (vma->anon_vma)
> >  		return;
> > --- a/mm/vma_internal.h~b
> > +++ a/mm/vma_internal.h
> > @@ -23,7 +23,6 @@
> >  #include <linux/ksm.h>
> >  #include <linux/khugepaged.h>
> >  #include <linux/list.h>
> > -#include <linux/major.h>
> >  #include <linux/maple_tree.h>
> >  #include <linux/mempolicy.h>
> >  #include <linux/mm.h>
> > --- a/tools/testing/selftests/mm/merge.c~b
> > +++ a/tools/testing/selftests/mm/merge.c
> > @@ -1324,7 +1324,7 @@ TEST_F(merge, anon_and_page_offset_misma
> >  	ASSERT_NE(ptr, MAP_FAILED);
> >
> >  	/*
> > -	 * Map another separately and trigger a CoW fault, at page offset 5:
> > +	 * Map another separately and trigger a CoW fault at page offset 5:
> >  	 *
> >  	 * |-----------|           |---------|
> >  	 * | unfaulted |           | faulted |
> > @@ -1362,110 +1362,6 @@ TEST_F(merge, anon_and_page_offset_misma
> >  	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 5 * page_size);
> >  }
> >
> > -TEST_F(merge, merge_map_private_dev_zero_unfaulted)
> > -{
> > -	struct procmap_fd *procmap = &self->procmap;
> > -	unsigned int page_size = self->page_size;
> > -	char *carveout = self->carveout;
> > -	char *ptr, *ptr2;
> > -	int fd_zero;
> > -
> > -	if (access("/dev/zero", F_OK))
> > -		SKIP(return, "No /dev/zero.");
> > -	fd_zero = open("/dev/zero", O_RDWR);
> > -	ASSERT_NE(fd_zero, -1);
> > -
> > -	/*
> > -	 * Map two MAP_PRIVATE-/dev/zero VMAs next to one another with offset 0
> > -	 * each.
> > -	 *
> > -	 * With these being made truly anonymous upon mapping, they will
> > -	 * merge. If they were file-backed VMAs the page offsets would prevent
> > -	 * merge:
> > -	 *
> > -	 * |-----||------|    |-------------|
> > -	 * | ptr || ptr2 | -> |     ptr     |
> > -	 * |-----||------|    |-------------|
> > -	 */
> > -	ptr = mmap(carveout, 5 * page_size, PROT_READ | PROT_WRITE,
> > -		   MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
> > -	if (ptr == MAP_FAILED) {
> > -		close(fd_zero);
> > -		ASSERT_TRUE(false);
> > -	}
> > -	ptr2 = mmap(&carveout[5 * page_size], 5 * page_size,
> > -		   PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
> > -	if (ptr2 == MAP_FAILED) {
> > -		close(fd_zero);
> > -		ASSERT_TRUE(false);
> > -	}
> > -	close(fd_zero);
> > -
> > -	/* Assert that they merged. */
> > -	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
> > -	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
> > -	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 10 * page_size);
> > -}
> > -
> > -TEST_F(merge, merge_map_private_dev_zero_faulted_unfaulted)
> > -{
> > -	struct procmap_fd *procmap = &self->procmap;
> > -	unsigned int page_size = self->page_size;
> > -	char *carveout = self->carveout;
> > -	char *ptr, *ptr2;
> > -	int fd_zero;
> > -
> > -	if (access("/dev/zero", F_OK))
> > -		SKIP(return, "No /dev/zero.");
> > -	fd_zero = open("/dev/zero", O_RDWR);
> > -	ASSERT_NE(fd_zero, -1);
> > -
> > -	/*
> > -	 * Map a MAP_PRIVATE mapping of /dev/zero with page offset 0, then fault
> > -	 * it in:
> > -	 *
> > -	 * |-------------------------------|
> > -	 * |           faulted             |
> > -	 * |-------------------------------|
> > -	 */
> > -	ptr = mmap(carveout, 15 * page_size, PROT_READ | PROT_WRITE,
> > -		   MAP_FIXED | MAP_PRIVATE, fd_zero, 0);
> > -	if (ptr == MAP_FAILED) {
> > -		close(fd_zero);
> > -		ASSERT_TRUE(false);
> > -	}
> > -	memset(ptr, 'x', 15 * page_size);
> > -
> > -	/*
> > -	 * Unmap the middle:
> > -	 *
> > -	 * |---------|           |---------|
> > -	 * | faulted |           | faulted |
> > -	 * |---------|           |---------|
> > -	 */
> > -	ASSERT_EQ(munmap(&ptr[5 * page_size], 5 * page_size), 0);
> > -
> > -	/*
> > -	 * Map in a new unfaulted mapping in the middle with page offset 0 -
> > -	 * this should merge and would not if it were treated as a file rather
> > -	 * than pure anon:
> > -	 *
> > -	 * |---------|-----------|---------|
> > -	 * | faulted | unfaulted | faulted |
> > -	 * |---------|-----------|---------|
> > -	 */
> > -	ptr2 = mmap(&carveout[5 * page_size], 5 * page_size,
> > -		    PROT_READ | PROT_WRITE, MAP_FIXED | MAP_PRIVATE,
> > -		    fd_zero, 0);
> > -	close(fd_zero);
> > -	ASSERT_NE(ptr2, MAP_FAILED);
> > -
> > -	/* Assert that they merged. */
> > -	ASSERT_TRUE(find_vma_procmap(procmap, ptr));
> > -	ASSERT_EQ(procmap->query.vma_start, (unsigned long)ptr);
> > -	ASSERT_EQ(procmap->query.vma_end, (unsigned long)ptr + 15 * page_size);
> > -}
> > -
> >  TEST_F(merge_with_fork, mremap_faulted_to_unfaulted_prev)
> >  {
> >  	struct procmap_fd *procmap = &self->procmap;
> > --- a/tools/testing/selftests/proc/proc-self-map-files-001.c~b
> > +++ a/tools/testing/selftests/proc/proc-self-map-files-001.c
> > @@ -51,7 +51,7 @@ int main(void)
> >  	int fd;
> >  	unsigned long a, b;
> >
> > -	fd = open("/proc/self/exe", O_RDONLY);
> > +	fd = open("/dev/zero", O_RDONLY);
> >  	if (fd == -1)
> >  		return 1;
> >
> > --- a/tools/testing/selftests/proc/proc-self-map-files-002.c~b
> > +++ a/tools/testing/selftests/proc/proc-self-map-files-002.c
> > @@ -57,7 +57,7 @@ int main(void)
> >  	int fd;
> >  	unsigned long a, b;
> >
> > -	fd = open("/proc/self/exe", O_RDONLY);
> > +	fd = open("/dev/zero", O_RDONLY);
> >  	if (fd == -1)
> >  		return 1;
> >
> > --- a/tools/testing/vma/include/dup.h~b
> > +++ a/tools/testing/vma/include/dup.h
> > @@ -15,21 +15,6 @@ struct task_struct *get_current(void);
> >  #define MMF_HAS_MDWE	28
> >  #define current get_current()
> >
> > -#define MINORBITS	20
> > -#define MINORMASK	((1U << MINORBITS) - 1)
> > -
> > -#define MAJOR(dev)	((unsigned int) ((dev) >> MINORBITS))
> > -#define MINOR(dev)	((unsigned int) ((dev) & MINORMASK))
> > -#define MKDEV(ma, mi)	(((ma) << MINORBITS) | (mi))
> > -
> > -#define S_IFMT  00170000
> > -#define S_IFCHR  0020000
> > -
> > -#define S_ISCHR(m)	(((m) & S_IFMT) == S_IFCHR)
> > -
> > -#define MEM_MAJOR		1
> > -#define DEVZERO_MINOR	5
> > -
> >  /*
> >   * Define the task command name length as enum, then it can be visible to
> >   * BPF programs.
> > @@ -38,8 +23,6 @@ enum {
> >  	TASK_COMM_LEN = 16,
> >  };
> >
> > -typedef unsigned short		umode_t;
> > -
> >  /* PARTIALLY implemented types. */
> >  struct mm_struct {
> >  	struct maple_tree mm_mt;
> > @@ -62,10 +45,6 @@ struct address_space {
> >  	unsigned long		flags;
> >  	atomic_t		i_mmap_writable;
> >  };
> > -struct inode {
> > -	umode_t			i_mode;
> > -	dev_t			i_rdev;
> > -};
> >  struct file_operations {
> >  	int (*mmap)(struct file *, struct vm_area_struct *);
> >  	int (*mmap_prepare)(struct vm_area_desc *);
> > @@ -73,7 +52,6 @@ struct file_operations {
> >  struct file {
> >  	struct address_space	*f_mapping;
> >  	const struct file_operations	*f_op;
> > -	struct inode			*f_inode;
> >  };
> >  struct anon_vma_chain {
> >  	struct anon_vma *anon_vma;
> > @@ -1660,23 +1638,9 @@ static inline pgoff_t linear_anon_page_i
> >  	const pgoff_t pgoff = __linear_anon_page_index(vma, address);
> >
> >  	VM_WARN_ON_ONCE(!vma_is_cow_mapping(vma));
> > -	if (vma_is_anonymous(vma))
> > +	/* Account for MAP_PRIVATE-/dev/zero which is only semi-anonymous. */
> > +	if (vma_is_anonymous(vma) && !vma->vm_file)
> >  		VM_WARN_ON_ONCE(pgoff != linear_page_index(vma, address));
> >
> >  	return pgoff;
> >  }
> > -
> > -static inline struct inode *file_inode(const struct file *f)
> > -{
> > -	return f->f_inode;
> > -}
> > -
> > -static inline unsigned iminor(const struct inode *inode)
> > -{
> > -	return MINOR(inode->i_rdev);
> > -}
> > -
> > -static inline unsigned imajor(const struct inode *inode)
> > -{
> > -	return MAJOR(inode->i_rdev);
> > -}
> > --- a/tools/testing/vma/tests/mmap.c~b
> > +++ a/tools/testing/vma/tests/mmap.c
> > @@ -45,57 +45,7 @@ static bool test_mmap_region_basic(void)
> >  	return true;
> >  }
> >
> > -static int dummy_mmap_prepare(struct vm_area_desc *desc)
> > -{
> > -	return 0;
> > -}
> > -
> > -static bool test_pure_anon_dev_zero(void)
> > -{
> > -	const vma_flags_t vma_flags = mk_vma_flags(VMA_READ_BIT, VMA_WRITE_BIT,
> > -			VMA_MAYREAD_BIT, VMA_MAYWRITE_BIT);
> > -	const struct file_operations f_op = {
> > -		.mmap_prepare = dummy_mmap_prepare,
> > -	};
> > -	struct inode inode = {
> > -		.i_mode = S_IFCHR,
> > -		.i_rdev = MKDEV(MEM_MAJOR, DEVZERO_MINOR),
> > -	};
> > -	struct file file = {
> > -		.f_inode = &inode,
> > -		.f_op = &f_op,
> > -	};
> > -	struct mm_struct mm = {};
> > -	struct vm_area_struct *vma;
> > -	unsigned long addr;
> > -	VMA_ITERATOR(vmi, &mm, 0);
> > -
> > -	current->mm = &mm;
> > -
> > -	/*
> > -	 * Map a MAP_PRIVATE-/dev/zero mapping at address 0x300000 with a page
> > -	 * offset of 0x10, which we expect to be reset to the anonymous page
> > -	 * offset.
> > -	 */
> > -	addr = __mmap_region(&file, 0x300000, 0x3000, vma_flags, 0x10, NULL);
> > -	ASSERT_EQ(addr, 0x300000);
> > -
> > -	/* Assert that it truly is an anonymous mapping. */
> > -	vma = vma_lookup(&mm, addr);
> > -	ASSERT_NE(vma, NULL);
> > -	ASSERT_TRUE(vma_is_anonymous(vma));
> > -	ASSERT_EQ(vma->vm_file, NULL);
> > -	ASSERT_EQ(vma->vm_private_data, NULL);
> > -	/* Expect anonymous page offsets. */
> > -	ASSERT_EQ(vma->vm_pgoff, 0x300);
> > -	ASSERT_EQ(vma_start_anon_pgoff(vma), 0x300);
> > -
> > -	cleanup_mm(&mm, &vmi);
> > -	return true;
> > -}
> > -
> >  static void run_mmap_tests(int *num_tests, int *num_fail)
> >  {
> >  	TEST(mmap_region_basic);
> > -	TEST(pure_anon_dev_zero);
> >  }
> > _
> >
> 
> --
> Cheers, Lorenzo