On 17-09-18 09:47 AM, 关云飞 wrote:
hello kefu chai, These two days I carefully considered the pr 17661 and looked the code about bufferlist and I still think the steps of 1-3 is needed. Although the ptr::_off can guarantee bufferlist to be copied/read/decode/write_file rightly, this will lead a bufferlist not clean and will waste memory like the picture in annex. Of course, it's also possible that i am not thinking about it, do you have any suggestions?
In your diagram, you show the case where allocated memory blocks are underutilized, wasting memory. If I understand you (and code from your PR) correctly, you want to move data from the middle of allocated blocks to front of them to reclaim memory - but the way you propose isn't any good really, you allocate new block of memory (and accompanying bufferptr), copy data from existing block to newly allocated one, then destroy old - this is very expensive CPU-wise, way more expensive than leaving these bytes wasted. Most of the time it wouldn't matter anyway, as most of bufferlists have limited lifetime and would get destroyed soon.
-- Piotr Dałek piotr.dalek@xxxxxxxxxxxx https://www.ovh.com/us/ -- To unsubscribe from this list: send the line "unsubscribe ceph-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
