Re: What do extra_free and extrastd_free params do in the dictionary object?

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On Thu, Jan 9, 2020 at 2:33 PM Xavi Hernandez <jahernan@xxxxxxxxxx> wrote:
On Thu, Jan 9, 2020 at 9:44 AM Amar Tumballi <amarts@xxxxxxxxx> wrote:


On Thu, Jan 9, 2020 at 1:38 PM Xavi Hernandez <jahernan@xxxxxxxxxx> wrote:
On Sun, Dec 22, 2019 at 4:56 PM Yaniv Kaul <ykaul@xxxxxxxxxx> wrote:
I could not find a relevant use for them. Can anyone enlighten me?

I'm not sure why they are needed. They seem to be used to keep the unserialized version of a dict around until the dict is destroyed. I thought this could be because we were using pointers to the unserialized data inside dict, but that's not the case currently. However, checking very old versions (pre 3.2), I see that dict values were not allocated, but a pointer to the unserialized data was used.

Xavi,

While you are right about the intent, it is used still, at least when I grepped latest repo to keep a reference in protocol layer. 

This is done to reduce a copy after the dictionary's binary content is received from RPC. The 'extra_free' flag is used when we use a GF_*ALLOC()'d buffer in protocol to receive dictionary, and extra_stdfree is used when RPC itself allocates the buffer and hence uses 'free()' to free the buffer.

I don't see it. When dict_unserialize() is called, key and value are allocated and copied, so  why do we need to keep the raw data after that ?

In 3.1 the value was simply a pointer to the unserialized data, but starting with 3.2, value is memdup'ed. Key is always copied. I don't see any other reference to the unserialized data right now. I think that instead of assigning the raw data to extra_(std)free, we should simply release that memory and remove those fields.

Am I missing something else ?

I did grep on 'extra_stdfree' and 'extra_free' and saw that many handshake/ and protocol code seemed to use it. Haven't gone deeper to check which part.

[amar@kadalu glusterfs]$ git grep extra_stdfree | wc -l
40
[amar@kadalu glusterfs]$ git grep extra_free | wc -l
5
 



I think this is not needed anymore. Probably we could remove these fields if that's the only reason.

If keeping them is hard to maintain, we can add few allocation to remove those elements, that shouldn't matter much IMO too. We are not using dictionary itself as protocol now (which we did in 1.x series though).

Regards,
Amar
---

 
TIA,
Y.
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