Decrease memory footprint of SessionData values #354
Closed
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Cookie is needed only during HRR and can be cleared afterwards.
Retained memory was unnecessarily large because of two reasons: * one reason was insufficiently evaluated fields sessionCipher and sessionCompression in SessionData values given to the session manager * another one was due to how ByteString-oriented extensions are decoded. ByteString pieces often share the same storage as a large input they are extracted from. Decoded extension values that are held in the context and given to the session manager are now copied to fresh storage in order to break the dependency to the network packet content.
| @@ -262,8 +262,9 @@ decodeServerName = runGetMaybe $ do | |||
| where | |||
| getServerName = do | |||
| ty <- getWord8 | |||
| sname <- getOpaque16 | |||
| let name = case ty of | |||
| snameParsed <- getOpaque16 | |||
There was a problem hiding this comment.
What about inserting B.copy to getOpaque16 (all functions using getBytes) intead of here?
There was a problem hiding this comment.
That would certainly work, but we have also many transient elements, only retained on the stack, or in the context shortly, for which we don't need copying. This is why I clear the cookie value for example.
|
4f8f014 looks good to me. |
kazu-yamamoto
approved these changes
Feb 4, 2019
|
In my opinion, internal data structures should be |
kazu-yamamoto
added a commit
to kazu-yamamoto/hs-tls
that referenced
this pull request
Feb 4, 2019
|
Merged. |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
The report in yesodweb/wai#728 shows a space leak in the session manager but also that retained memory is high overall.
Here are simple mitigations, mainly to decrease what is retained by SessionData values. This kind of modification can probably be carried out further to decrease footprint of live Context values.
With this PR I measure process memory on the server memleak test going down to 24 KB per session instead of 54 KB.
As for design, copying ByteStrings ideally should be moved out of extension decoding but this is a very convenient location (before additional transformations take place, like unpacking to String).