Re: [PATCH 5/6] block/block-copy: add memory limit

[Max Reitz <mreitz@redhat.com>]

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On 07.10.19 19:10, Vladimir Sementsov-Ogievskiy wrote:
> 07.10.2019 18:27, Max Reitz wrote:
>> On 03.10.19 19:15, Vladimir Sementsov-Ogievskiy wrote:
>>> Currently total allocation for parallel requests to block-copy instance
>>> is unlimited. Let's limit it to 128 MiB.
>>>
>>> For now block-copy is used only in backup, so actually we limit total
>>> allocation for backup job.
>>>
>>> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
>>> ---
>>>   include/block/block-copy.h | 3 +++
>>>   block/block-copy.c         | 5 +++++
>>>   2 files changed, 8 insertions(+)
>>>
>>> diff --git a/include/block/block-copy.h b/include/block/block-copy.h
>>> index e2e135ff1b..bb666e7068 100644
>>> --- a/include/block/block-copy.h
>>> +++ b/include/block/block-copy.h
>>> @@ -16,6 +16,7 @@
>>>   #define BLOCK_COPY_H
>>>   
>>>   #include "block/block.h"
>>> +#include "qemu/co-shared-amount.h"
>>>   
>>>   typedef struct BlockCopyInFlightReq {
>>>       int64_t start_byte;
>>> @@ -69,6 +70,8 @@ typedef struct BlockCopyState {
>>>        */
>>>       ProgressResetCallbackFunc progress_reset_callback;
>>>       void *progress_opaque;
>>> +
>>> +    QemuCoSharedAmount *mem;
>>>   } BlockCopyState;
>>>   
>>>   BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
>>> diff --git a/block/block-copy.c b/block/block-copy.c
>>> index cc49d2345d..e700c20d0f 100644
>>> --- a/block/block-copy.c
>>> +++ b/block/block-copy.c
>>> @@ -21,6 +21,7 @@
>>>   #include "qemu/units.h"
>>>   
>>>   #define BLOCK_COPY_MAX_COPY_RANGE (16 * MiB)
>>> +#define BLOCK_COPY_MAX_MEM (128 * MiB)
>>>   
>>>   static void coroutine_fn block_copy_wait_inflight_reqs(BlockCopyState *s,
>>>                                                          int64_t start,
>>> @@ -64,6 +65,7 @@ void block_copy_state_free(BlockCopyState *s)
>>>       }
>>>   
>>>       bdrv_release_dirty_bitmap(s->source->bs, s->copy_bitmap);
>>> +    qemu_co_shared_amount_free(s->mem);
>>>       g_free(s);
>>>   }
>>>   
>>> @@ -95,6 +97,7 @@ BlockCopyState *block_copy_state_new(BdrvChild *source, BdrvChild *target,
>>>           .cluster_size = cluster_size,
>>>           .len = bdrv_dirty_bitmap_size(copy_bitmap),
>>>           .write_flags = write_flags,
>>> +        .mem = qemu_co_shared_amount_new(BLOCK_COPY_MAX_MEM),
>>>       };
>>>   
>>>       s->copy_range_size = QEMU_ALIGN_DOWN(max_transfer, cluster_size),
>>> @@ -316,7 +319,9 @@ int coroutine_fn block_copy(BlockCopyState *s,
>>>   
>>>           bdrv_reset_dirty_bitmap(s->copy_bitmap, start, chunk_end - start);
>>>   
>>> +        qemu_co_get_amount(s->mem, chunk_end - start);
>>
>> Now that I see it like this, maybe the name is too short.  This sounds
>> like it was trying to get some amount of coroutines.
>>
>> Would “qemu_co_get_from_shared_amount” be too long?  (Something like
>> qemu_co_sham_alloc() would be funny, but maybe not.  :-)  Or maybe
>> exactly because it”s funny.)
>>
> 
> hmm sham may be interpreted as shared memory, not only like shame..

“sham” is also a word by itself. :-)

> And if we call it _alloc, the opposite should be _free, but how to
> distinguish it from freeing the whole object? Hmm, use create/destroy for
> the whole object maybe.
> 
> May be, drop "qemu_" ? It's not very informative. Or may be drop "co_"?.
> 
> I don't like shaming my shared amount :)

It’s worse calling it all a sham.

> May be, we should imagine, what are we allocating? May be balls?
> 
> struct BallAllocator
> 
> ball_allocator_create
> ball_allocator_destroy
> 
> co_try_alloc_balls
> co_alloc_balls
> co_free_balls
> 
> Or bars? Or which thing may be used for funny naming and to not intersect
> with existing concepts like memory?

I love it (thanks for making my morning), but I fear it may be
interpreted as risqué.

Maybe just shres for shared resource?  So alloc_from_shres?

Max

>>
>>>           ret = block_copy_do_copy(s, start, chunk_end, error_is_read);
>>> +        qemu_co_put_amount(s->mem, chunk_end - start);
>>>           if (ret < 0) {
>>>               bdrv_set_dirty_bitmap(s->copy_bitmap, start, chunk_end - start);
>>>               break;
>>>
>>
>>
> 
> 



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