Nicholas Piggin <npig...@gmail.com> writes:
> On Thu, 21 Jun 2018 14:28:22 -0700
> Matthew Wilcox <wi...@infradead.org> wrote:
>
>> ida_alloc_range is the perfect fit for this use case. Eliminates
>> a custom spinlock, a call to ida_pre_get and a local check for the
>> allocated ID exceeding a maximum.
>>
>> Signed-off-by: Matthew Wilcox <wi...@infradead.org>
>> ---
>> arch/powerpc/mm/mmu_context_book3s64.c | 44 +++-----------------------
>> 1 file changed, 4 insertions(+), 40 deletions(-)
>>
>> diff --git a/arch/powerpc/mm/mmu_context_book3s64.c
>> b/arch/powerpc/mm/mmu_context_book3s64.c
>> index f3d4b4a0e561..5a0cf2cc8ba0 100644
>> --- a/arch/powerpc/mm/mmu_context_book3s64.c
>> +++ b/arch/powerpc/mm/mmu_context_book3s64.c
>> @@ -26,48 +26,16 @@
>> #include <asm/mmu_context.h>
>> #include <asm/pgalloc.h>
>>
>> -static DEFINE_SPINLOCK(mmu_context_lock);
>> static DEFINE_IDA(mmu_context_ida);
>>
>> static int alloc_context_id(int min_id, int max_id)
>> {
>> - int index, err;
>> -
>> -again:
>> - if (!ida_pre_get(&mmu_context_ida, GFP_KERNEL))
>> - return -ENOMEM;
>> -
>> - spin_lock(&mmu_context_lock);
>> - err = ida_get_new_above(&mmu_context_ida, min_id, &index);
>> - spin_unlock(&mmu_context_lock);
>> -
>> - if (err == -EAGAIN)
>> - goto again;
>> - else if (err)
>> - return err;
>> -
>> - if (index > max_id) {
>> - spin_lock(&mmu_context_lock);
>> - ida_remove(&mmu_context_ida, index);
>> - spin_unlock(&mmu_context_lock);
>> - return -ENOMEM;
>> - }
>> -
>> - return index;
>> + return ida_alloc_range(&mmu_context_ida, min_id, max_id, GFP_KERNEL);
>> }
>>
>> void hash__reserve_context_id(int id)
>> {
>> - int rc, result = 0;
>> -
>> - do {
>> - if (!ida_pre_get(&mmu_context_ida, GFP_KERNEL))
>> - break;
>> -
>> - spin_lock(&mmu_context_lock);
>> - rc = ida_get_new_above(&mmu_context_ida, id, &result);
>> - spin_unlock(&mmu_context_lock);
>> - } while (rc == -EAGAIN);
>> + int result = ida_alloc_range(&mmu_context_ida, id, id, GFP_KERNEL);
>>
>> WARN(result != id, "mmu: Failed to reserve context id %d (rc %d)\n",
>> id, result);
>> }
>> @@ -172,9 +140,7 @@ int init_new_context(struct task_struct *tsk, struct
>> mm_struct *mm)
>>
>> void __destroy_context(int context_id)
>> {
>> - spin_lock(&mmu_context_lock);
>> - ida_remove(&mmu_context_ida, context_id);
>> - spin_unlock(&mmu_context_lock);
>> + ida_free(&mmu_context_ida, context_id);
>> }
>> EXPORT_SYMBOL_GPL(__destroy_context);
>>
>> @@ -182,13 +148,11 @@ static void destroy_contexts(mm_context_t *ctx)
>> {
>> int index, context_id;
>>
>> - spin_lock(&mmu_context_lock);
>> for (index = 0; index < ARRAY_SIZE(ctx->extended_id); index++) {
>> context_id = ctx->extended_id[index];
>> if (context_id)
>> - ida_remove(&mmu_context_ida, context_id);
>> + ida_free(&mmu_context_ida, context_id);
>> }
>> - spin_unlock(&mmu_context_lock);
>> }
>>
>> static void pte_frag_destroy(void *pte_frag)
>
> This hunk should be okay because the mmu_context_lock does not protect
> the extended_id array, right Aneesh?
Yes. This is called at process exit, so we should not find parallel
calls. On the allocation side, we are protected by mmap_sem. We do
allocate extended_id when doing mmap.
-aneesh
