On 2018/09/22 8:21, Andrew Morton wrote: > On Thu, 20 Sep 2018 19:33:15 -0400 Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote: > >> On Thu, Sep 20, 2018 at 5:12 PM Todd Kjos <tkjos@xxxxxxxxxx> wrote: >>> >>> +Joel Fernandes >>> >>> On Thu, Sep 20, 2018 at 2:11 PM Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote: >>>> >>>> >>>> Thanks. Let's cc the ashmem folks. >>>> >> >> This should be fixed by https://patchwork.kernel.org/patch/10572477/ >> >> It has Neil Brown's Reviewed-by but looks like didn't yet appear in >> anyone's tree, could Greg take this patch? > > All is well. That went into mainline yesterday, with a cc:stable. > This problem was not fixed at all. Why do we need to call fallocate() synchronously with ashmem_mutex held? Why can't we call fallocate() asynchronously from WQ_MEM_RECLAIM workqueue context so that we can call fallocate() with ashmem_mutex not held? I don't know how ashmem works, but as far as I can guess, offloading is possible as long as other operations which depend on the completion of fallocate() operation (e.g. read()/mmap(), querying/changing pinned status) wait for completion of asynchronous fallocate() operation (like a draft patch shown below is doing). --- drivers/staging/android/ashmem.c | 50 ++++++++++++++++++++++++++++---- 1 file changed, 45 insertions(+), 5 deletions(-) diff --git a/drivers/staging/android/ashmem.c b/drivers/staging/android/ashmem.c index 90a8a9f1ac7d..1a890c43a10a 100644 --- a/drivers/staging/android/ashmem.c +++ b/drivers/staging/android/ashmem.c @@ -75,6 +75,17 @@ struct ashmem_range { /* LRU list of unpinned pages, protected by ashmem_mutex */ static LIST_HEAD(ashmem_lru_list); +static struct workqueue_struct *ashmem_wq; +static atomic_t ashmem_shrink_inflight = ATOMIC_INIT(0); +static DECLARE_WAIT_QUEUE_HEAD(ashmem_shrink_wait); + +struct ashmem_shrink_work { + struct work_struct work; + struct file *file; + loff_t start; + loff_t end; +}; + /* * long lru_count - The count of pages on our LRU list. * @@ -292,6 +303,7 @@ static ssize_t ashmem_read_iter(struct kiocb *iocb, struct iov_iter *iter) int ret = 0; mutex_lock(&ashmem_mutex); + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); /* If size is not set, or set to 0, always return EOF. */ if (asma->size == 0) @@ -359,6 +371,7 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) int ret = 0; mutex_lock(&ashmem_mutex); + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); /* user needs to SET_SIZE before mapping */ if (!asma->size) { @@ -421,6 +434,19 @@ static int ashmem_mmap(struct file *file, struct vm_area_struct *vma) return ret; } +static void ashmem_shrink_worker(struct work_struct *work) +{ + struct ashmem_shrink_work *w = container_of(work, typeof(*w), work); + + w->file->f_op->fallocate(w->file, + FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, + w->start, w->end - w->start); + fput(w->file); + kfree(w); + if (atomic_dec_and_test(&ashmem_shrink_inflight)) + wake_up_all(&ashmem_shrink_wait); +} + /* * ashmem_shrink - our cache shrinker, called from mm/vmscan.c * @@ -449,12 +475,18 @@ ashmem_shrink_scan(struct shrinker *shrink, struct shrink_control *sc) return -1; 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; + struct ashmem_shrink_work *w = kzalloc(sizeof(*w), GFP_ATOMIC); + + if (!w) + break; + INIT_WORK(&w->work, ashmem_shrink_worker); + w->file = range->asma->file; + get_file(w->file); + w->start = range->pgstart * PAGE_SIZE; + w->end = (range->pgend + 1) * PAGE_SIZE; + atomic_inc(&ashmem_shrink_inflight); + queue_work(ashmem_wq, &w->work); - range->asma->file->f_op->fallocate(range->asma->file, - FALLOC_FL_PUNCH_HOLE | FALLOC_FL_KEEP_SIZE, - start, end - start); range->purged = ASHMEM_WAS_PURGED; lru_del(range); @@ -713,6 +745,7 @@ static int ashmem_pin_unpin(struct ashmem_area *asma, unsigned long cmd, return -EFAULT; mutex_lock(&ashmem_mutex); + wait_event(ashmem_shrink_wait, !atomic_read(&ashmem_shrink_inflight)); if (!asma->file) goto out_unlock; @@ -883,8 +916,15 @@ static int __init ashmem_init(void) goto out_free2; } + ashmem_wq = alloc_workqueue("ashmem_wq", WQ_MEM_RECLAIM, 0); + if (!ashmem_wq) { + pr_err("failed to create workqueue\n"); + goto out_demisc; + } + ret = register_shrinker(&ashmem_shrinker); if (ret) { + destroy_workqueue(ashmem_wq); pr_err("failed to register shrinker!\n"); goto out_demisc; } -- 2.17.1
