[Sheepdog] [PATCH] sheep: reduce snapshot COW read/write

[Liu Yuan]

On 03/22/2012 04:40 PM, yaohaiting.wujue at gmail.com wrote:

> From: HaiTing Yao <wujue.yht at taobao.com>
> 
> Doing snapshot COW:
> 
> 1, If new writing request occurs and need COW for sanpshot, now read old
> object to buffer, then write the buffer to new object, then write the
> request data to new object. We can merge the latter two writing request.
> 
> 2, If new writing request covers whole object, no need to read old
> object.
> 
> After the modification, pass bigger buffer to do_write_obj when doing
> COW, but it will not add the burden. COW is never for inode object, so
> it will not use the journal.
> 
> Signed-off-by: HaiTing Yao <wujue.yht at taobao.com>
> ---
>  sheep/store.c |   29 +++++++++++++++++------------
>  1 files changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/sheep/store.c b/sheep/store.c
> index dfec235..97f1f13 100644
> --- a/sheep/store.c
> +++ b/sheep/store.c
> @@ -640,6 +640,7 @@ int store_create_and_write_obj(const struct sd_req *req, struct sd_rsp *rsp, voi
>  {
>  	struct sd_obj_req *hdr = (struct sd_obj_req *)req;
>  	struct request *request = (struct request *)data;
> +	struct sd_obj_req cow_hdr;
>  	int ret;
>  	uint32_t epoch = hdr->epoch;
>  	char *buf = NULL;
> @@ -664,19 +665,23 @@ int store_create_and_write_obj(const struct sd_req *req, struct sd_rsp *rsp, voi
>  		dprintf("%" PRIu64 ", %" PRIx64 "\n", hdr->oid, hdr->cow_oid);
>  
>  		buf = xzalloc(SD_DATA_OBJ_SIZE);
> -		ret = read_copy_from_cluster(request, hdr->epoch, hdr->cow_oid, buf);
> -		if (ret != SD_RES_SUCCESS) {
> -			eprintf("failed to read cow object\n");
> -			goto out;
> +		if ((hdr->data_length != SD_DATA_OBJ_SIZE)
> +			|| (hdr->offset!= 0)) {


For create_and_write object, data_length of request is always
SD_DATA_OBJ_SIZE and offset always 0.

Thanks,
Yuan

> +			ret = read_copy_from_cluster(request, hdr->epoch, hdr->cow_oid, buf);
> +			if (ret != SD_RES_SUCCESS) {
> +				eprintf("failed to read cow object\n");
> +				goto out;
> +			}
>  		}
> -		iocb.buf = buf;
> -		iocb.length = SD_DATA_OBJ_SIZE;
> -		iocb.offset = 0;
> -		ret = sd_store->write(hdr->oid, &iocb);
> -		if (ret != SD_RES_SUCCESS)
> -			goto out;
> -	}
> -	ret = do_write_obj(&iocb, hdr, epoch, request->data);
> +
> +		memcpy(buf + hdr->offset, request->data, hdr->data_length);
> +		memcpy(&cow_hdr, hdr, sizeof(cow_hdr));
> +		cow_hdr.offset = 0;
> +		cow_hdr.data_length = SD_DATA_OBJ_SIZE;
> +
> +		ret = do_write_obj(&iocb, &cow_hdr, epoch, buf);
> +	} else
> +		ret = do_write_obj(&iocb, hdr, epoch, request->data);
>  out:
>  	free(buf);
>  	sd_store->close(hdr->oid, &iocb);