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Subject[PATCH 4/6] [RFC] ashmem: Convert ashmem to use volatile ranges
Date
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: Taras Glek <tgek@mozilla.com>
CC: Mike Hommey <mh@glandium.org>
CC: Jan Kara <jack@suse.cz>
CC: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
---
drivers/staging/android/ashmem.c | 331 +------------------------------------
1 files changed, 9 insertions(+), 322 deletions(-)

diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c
index e84dbec..9e8fe37 100644
--- a/drivers/staging/android/ashmem.c
+++ b/drivers/staging/android/ashmem.c
@@ -50,26 +50,6 @@ 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
@@ -77,102 +57,9 @@ 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)
{
@@ -198,12 +85,6 @@ 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);
@@ -337,56 +218,6 @@ 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;
@@ -459,136 +290,10 @@ 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))
@@ -610,20 +315,24 @@ 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;
}

@@ -667,15 +376,6 @@ 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;
}

@@ -711,22 +411,12 @@ 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)) {
- printk(KERN_ERR "ashmem: failed to create slab cache\n");
- return -ENOMEM;
- }
-
ret = misc_register(&ashmem_misc);
if (unlikely(ret)) {
printk(KERN_ERR "ashmem: failed to register misc device!\n");
return ret;
}

- register_shrinker(&ashmem_shrinker);
-
printk(KERN_INFO "ashmem: initialized\n");

return 0;
@@ -736,13 +426,10 @@ static void __exit ashmem_exit(void)
{
int ret;

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

- kmem_cache_destroy(ashmem_range_cachep);
kmem_cache_destroy(ashmem_area_cachep);

printk(KERN_INFO "ashmem: unloaded\n");
--
1.7.3.2.146.gca209


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