[PATCH 3/5] [RFC] ashmem: Convert ashmem to use volatile ranges

John Stultz
2012-07-28T03:59:15Z

Rework of my first pass attempt at getting ashmem to utilize
the volatile range code, now using the fallocate interface.

In this implementaiton GET_PIN_STATUS is unimplemented, due to
the fact that adding a ISVOLATILE check wasn't considered
terribly useful in earlier reviews. It would be trivial to
re-add that functionality, but I wanted to check w/ the
Android developers to see how often GET_PIN_STATUS is actually
used?

Similarly the ashmem PURGE_ALL_CACHES ioctl does not function,
as the volatile range purging is no longer directly under its
control.

CC: Andrew Morton <akpm@linux-foundation.org>
CC: Android Kernel Team <kernel-team@android.com>
CC: Robert Love <rlove@google.com>
CC: Mel Gorman <mel@csn.ul.ie>
CC: Hugh Dickins <hughd@google.com>
CC: Dave Hansen <dave@linux.vnet.ibm.com>
CC: Rik van Riel <riel@redhat.com>
CC: Dmitry Adamushko <dmitry.adamushko@gmail.com>
CC: Dave Chinner <david@fromorbit.com>
CC: Neil Brown <neilb@suse.de>
CC: Andrea Righi <andrea@betterlinux.com>
CC: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
CC: Mike Hommey <mh@glandium.org>
CC: Jan Kara <jack@suse.cz>
CC: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
CC: Michel Lespinasse <walken@google.com>
CC: Minchan Kim <minchan@kernel.org>
CC: linux-mm@kvack.org <linux-mm@kvack.org>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
drivers/staging/android/ashmem.c | 331 ++------------------------------------
1 file changed, 10 insertions(+), 321 deletions(-)

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index 69cf2db..6ce73e1 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -52,26 +52,6 @@ struct ashmem_area {
};

/*
- * ashmem_range - represents an interval of unpinned (evictable) pages
- * Lifecycle: From unpin to pin
- * Locking: Protected by `ashmem_mutex'
- */
-struct ashmem_range {
- struct list_head lru; /* entry in LRU list */
- struct list_head unpinned; /* entry in its area's unpinned list */
- struct ashmem_area *asma; /* associated area */
- size_t pgstart; /* starting page, inclusive */
- size_t pgend; /* ending page, inclusive */
- unsigned int purged; /* ASHMEM_NOT or ASHMEM_WAS_PURGED */
-};
-
-/* LRU list of unpinned pages, protected by ashmem_mutex */
-static LIST_HEAD(ashmem_lru_list);
-
-/* Count of pages on our LRU list, protected by ashmem_mutex */
-static unsigned long lru_count;
-
-/*
* ashmem_mutex - protects the list of and each individual ashmem_area
*
* Lock Ordering: ashmex_mutex -> i_mutex -> i_alloc_sem
@@ -79,102 +59,9 @@ static unsigned long lru_count;
static DEFINE_MUTEX(ashmem_mutex);

static struct kmem_cache *ashmem_area_cachep __read_mostly;
-static struct kmem_cache *ashmem_range_cachep __read_mostly;
-
-#define range_size(range) \
- ((range)->pgend - (range)->pgstart + 1)
-
-#define range_on_lru(range) \
- ((range)->purged == ASHMEM_NOT_PURGED)
-
-#define page_range_subsumes_range(range, start, end) \
- (((range)->pgstart >= (start)) && ((range)->pgend <= (end)))
-
-#define page_range_subsumed_by_range(range, start, end) \
- (((range)->pgstart <= (start)) && ((range)->pgend >= (end)))
-
-#define page_in_range(range, page) \
- (((range)->pgstart <= (page)) && ((range)->pgend >= (page)))
-
-#define page_range_in_range(range, start, end) \
- (page_in_range(range, start) || page_in_range(range, end) || \
- page_range_subsumes_range(range, start, end))
-
-#define range_before_page(range, page) \
- ((range)->pgend < (page))

#define PROT_MASK (PROT_EXEC | PROT_READ | PROT_WRITE)

-static inline void lru_add(struct ashmem_range *range)
-{
- list_add_tail(&range->lru, &ashmem_lru_list);
- lru_count += range_size(range);
-}
-
-static inline void lru_del(struct ashmem_range *range)
-{
- list_del(&range->lru);
- lru_count -= range_size(range);
-}
-
-/*
- * range_alloc - allocate and initialize a new ashmem_range structure
- *
- * 'asma' - associated ashmem_area
- * 'prev_range' - the previous ashmem_range in the sorted asma->unpinned list
- * 'purged' - initial purge value (ASMEM_NOT_PURGED or ASHMEM_WAS_PURGED)
- * 'start' - starting page, inclusive
- * 'end' - ending page, inclusive
- *
- * Caller must hold ashmem_mutex.
- */
-static int range_alloc(struct ashmem_area *asma,
- struct ashmem_range *prev_range, unsigned int purged,
- size_t start, size_t end)
-{
- struct ashmem_range *range;
-
- range = kmem_cache_zalloc(ashmem_range_cachep, GFP_KERNEL);
- if (unlikely(!range))
- return -ENOMEM;
-
- range->asma = asma;
- range->pgstart = start;
- range->pgend = end;
- range->purged = purged;
-
- list_add_tail(&range->unpinned, &prev_range->unpinned);
-
- if (range_on_lru(range))
- lru_add(range);
-
- return 0;
-}
-
-static void range_del(struct ashmem_range *range)
-{
- list_del(&range->unpinned);
- if (range_on_lru(range))
- lru_del(range);
- kmem_cache_free(ashmem_range_cachep, range);
-}
-
-/*
- * range_shrink - shrinks a range
- *
- * Caller must hold ashmem_mutex.
- */
-static inline void range_shrink(struct ashmem_range *range,
- size_t start, size_t end)
-{
- size_t pre = range_size(range);
-
- range->pgstart = start;
- range->pgend = end;
-
- if (range_on_lru(range))
- lru_count -= pre - range_size(range);
-}

static int ashmem_open(struct inode *inode, struct file *file)
{
@@ -200,12 +87,6 @@ static int ashmem_open(struct inode *inode, struct file *file)
static int ashmem_release(struct inode *ignored, struct file *file)
{
struct ashmem_area *asma = file->private_data;
- struct ashmem_range *range, *next;
-
- mutex_lock(&ashmem_mutex);
- list_for_each_entry_safe(range, next, &asma->unpinned_list, unpinned)
- range_del(range);
- mutex_unlock(&ashmem_mutex);

if (asma->file)
fput(asma->file);
@@ -339,56 +220,6 @@ out:
return ret;
}

-/*
- * ashmem_shrink - our cache shrinker, called from mm/vmscan.c :: shrink_slab
- *
- * 'nr_to_scan' is the number of objects (pages) to prune, or 0 to query how
- * many objects (pages) we have in total.
- *
- * 'gfp_mask' is the mask of the allocation that got us into this mess.
- *
- * Return value is the number of objects (pages) remaining, or -1 if we cannot
- * proceed without risk of deadlock (due to gfp_mask).
- *
- * We approximate LRU via least-recently-unpinned, jettisoning unpinned partial
- * chunks of ashmem regions LRU-wise one-at-a-time until we hit 'nr_to_scan'
- * pages freed.
- */
-static int ashmem_shrink(struct shrinker *s, struct shrink_control *sc)
-{
- struct ashmem_range *range, *next;
-
- /* We might recurse into filesystem code, so bail out if necessary */
- if (sc->nr_to_scan && !(sc->gfp_mask & __GFP_FS))
- return -1;
- if (!sc->nr_to_scan)
- return lru_count;
-
- mutex_lock(&ashmem_mutex);
- list_for_each_entry_safe(range, next, &ashmem_lru_list, lru) {
- loff_t start = range->pgstart * PAGE_SIZE;
- loff_t end = (range->pgend + 1) * PAGE_SIZE;
-
- do_fallocate(range->asma->file,
- FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE,
- start, end - start);
- range->purged = ASHMEM_WAS_PURGED;
- lru_del(range);
-
- sc->nr_to_scan -= range_size(range);
- if (sc->nr_to_scan <= 0)
- break;
- }
- mutex_unlock(&ashmem_mutex);
-
- return lru_count;
-}
-
-static struct shrinker ashmem_shrinker = {
- .shrink = ashmem_shrink,
- .seeks = DEFAULT_SEEKS * 4,
-};
-
static int set_prot_mask(struct ashmem_area *asma, unsigned long prot)
{
int ret = 0;
@@ -461,136 +292,10 @@ static int get_name(struct ashmem_area *asma, void __user *name)
return ret;
}

-/*
- * ashmem_pin - pin the given ashmem region, returning whether it was
- * previously purged (ASHMEM_WAS_PURGED) or not (ASHMEM_NOT_PURGED).
- *
- * Caller must hold ashmem_mutex.
- */
-static int ashmem_pin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
-{
- struct ashmem_range *range, *next;
- int ret = ASHMEM_NOT_PURGED;
-
- list_for_each_entry_safe(range, next, &asma->unpinned_list, unpinned) {
- /* moved past last applicable page; we can short circuit */
- if (range_before_page(range, pgstart))
- break;
-
- /*
- * The user can ask us to pin pages that span multiple ranges,
- * or to pin pages that aren't even unpinned, so this is messy.
- *
- * Four cases:
- * 1. The requested range subsumes an existing range, so we
- * just remove the entire matching range.
- * 2. The requested range overlaps the start of an existing
- * range, so we just update that range.
- * 3. The requested range overlaps the end of an existing
- * range, so we just update that range.
- * 4. The requested range punches a hole in an existing range,
- * so we have to update one side of the range and then
- * create a new range for the other side.
- */
- if (page_range_in_range(range, pgstart, pgend)) {
- ret |= range->purged;
-
- /* Case #1: Easy. Just nuke the whole thing. */
- if (page_range_subsumes_range(range, pgstart, pgend)) {
- range_del(range);
- continue;
- }
-
- /* Case #2: We overlap from the start, so adjust it */
- if (range->pgstart >= pgstart) {
- range_shrink(range, pgend + 1, range->pgend);
- continue;
- }
-
- /* Case #3: We overlap from the rear, so adjust it */
- if (range->pgend <= pgend) {
- range_shrink(range, range->pgstart, pgstart-1);
- continue;
- }
-
- /*
- * Case #4: We eat a chunk out of the middle. A bit
- * more complicated, we allocate a new range for the
- * second half and adjust the first chunk's endpoint.
- */
- range_alloc(asma, range, range->purged,
- pgend + 1, range->pgend);
- range_shrink(range, range->pgstart, pgstart - 1);
- break;
- }
- }
-
- return ret;
-}
-
-/*
- * ashmem_unpin - unpin the given range of pages. Returns zero on success.
- *
- * Caller must hold ashmem_mutex.
- */
-static int ashmem_unpin(struct ashmem_area *asma, size_t pgstart, size_t pgend)
-{
- struct ashmem_range *range, *next;
- unsigned int purged = ASHMEM_NOT_PURGED;
-
-restart:
- list_for_each_entry_safe(range, next, &asma->unpinned_list, unpinned) {
- /* short circuit: this is our insertion point */
- if (range_before_page(range, pgstart))
- break;
-
- /*
- * The user can ask us to unpin pages that are already entirely
- * or partially pinned. We handle those two cases here.
- */
- if (page_range_subsumed_by_range(range, pgstart, pgend))
- return 0;
- if (page_range_in_range(range, pgstart, pgend)) {
- pgstart = min_t(size_t, range->pgstart, pgstart),
- pgend = max_t(size_t, range->pgend, pgend);
- purged |= range->purged;
- range_del(range);
- goto restart;
- }
- }
-
- return range_alloc(asma, range, purged, pgstart, pgend);
-}
-
-/*
- * ashmem_get_pin_status - Returns ASHMEM_IS_UNPINNED if _any_ pages in the
- * given interval are unpinned and ASHMEM_IS_PINNED otherwise.
- *
- * Caller must hold ashmem_mutex.
- */
-static int ashmem_get_pin_status(struct ashmem_area *asma, size_t pgstart,
- size_t pgend)
-{
- struct ashmem_range *range;
- int ret = ASHMEM_IS_PINNED;
-
- list_for_each_entry(range, &asma->unpinned_list, unpinned) {
- if (range_before_page(range, pgstart))
- break;
- if (page_range_in_range(range, pgstart, pgend)) {
- ret = ASHMEM_IS_UNPINNED;
- break;
- }
- }
-
- return ret;
-}
-
static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
void __user *p)
{
struct ashmem_pin pin;
- size_t pgstart, pgend;
int ret = -EINVAL;

if (unlikely(!asma->file))
@@ -612,20 +317,24 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd,
if (unlikely(PAGE_ALIGN(asma->size) < pin.offset + pin.len))
return -EINVAL;

- pgstart = pin.offset / PAGE_SIZE;
- pgend = pgstart + (pin.len / PAGE_SIZE) - 1;

mutex_lock(&ashmem_mutex);

switch (cmd) {
case ASHMEM_PIN:
- ret = ashmem_pin(asma, pgstart, pgend);
+ ret = do_fallocate(asma->file, FALLOC_FL_MARK_VOLATILE,
+ pin.offset, pin.len);
break;
case ASHMEM_UNPIN:
- ret = ashmem_unpin(asma, pgstart, pgend);
+ ret = do_fallocate(asma->file, FALLOC_FL_UNMARK_VOLATILE,
+ pin.offset, pin.len);
break;
case ASHMEM_GET_PIN_STATUS:
- ret = ashmem_get_pin_status(asma, pgstart, pgend);
+ /*
+ * XXX - volatile ranges currently don't provide status,
+ * due to questionable utility
+ */
+ ret = -EINVAL;
break;
}

@@ -669,15 +378,6 @@ static long ashmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
break;
case ASHMEM_PURGE_ALL_CACHES:
ret = -EPERM;
- if (capable(CAP_SYS_ADMIN)) {
- struct shrink_control sc = {
- .gfp_mask = GFP_KERNEL,
- .nr_to_scan = 0,
- };
- ret = ashmem_shrink(&ashmem_shrinker, &sc);
- sc.nr_to_scan = ret;
- ashmem_shrink(&ashmem_shrinker, &sc);
- }
break;
}

@@ -713,21 +413,13 @@ static int __init ashmem_init(void)
return -ENOMEM;
}

- ashmem_range_cachep = kmem_cache_create("ashmem_range_cache",
- sizeof(struct ashmem_range),
- 0, 0, NULL);
- if (unlikely(!ashmem_range_cachep)) {
- pr_err("failed to create slab cache\n");
- return -ENOMEM;
- }
-
ret = misc_register(&ashmem_misc);
if (unlikely(ret)) {
pr_err("failed to register misc device!\n");
return ret;
}

- register_shrinker(&ashmem_shrinker);
+

pr_info("initialized\n");

@@ -738,13 +430,10 @@ static void __exit ashmem_exit(void)
{
int ret;

- unregister_shrinker(&ashmem_shrinker);
-
ret = misc_deregister(&ashmem_misc);
if (unlikely(ret))
pr_err("failed to unregister misc device!\n");

- kmem_cache_destroy(ashmem_range_cachep);
kmem_cache_destroy(ashmem_area_cachep);

pr_info("unloaded\n");
--
1.7.9.5