add git-annex filter-process

filter-process: New command that can make git add/checkout faster when
there are a lot of unlocked annexed files or non-annexed files, but that
also makes git add of large annexed files slower.

Use it by running: git
config filter.annex.process 'git-annex filter-process'

Fully tested and working, but I have not benchmarked it at all.
And, incremental hashing is not done when git add uses it, so extra work is
done in that case.

Sponsored-by: Mark Reidenbach on Patreon

CHANGELOG

@@ -4,6 +4,10 @@ git-annex (8.20211029) UNRELEASED; urgency=medium
     instead output a blank line like other batch commands do.
   * metadata --batch --json: Reject input whose "fields" does not consist
     of arrays of strings. Such invalid input used to be silently ignored.
+  * filter-process: New command that can make git add/checkout faster when
+    there are a lot of unlocked annexed files or non-annexed files, but that
+    also makes git add of large annexed files slower. Use it by running:
+    git config filter.annex.process 'git-annex filter-process'
 
  -- Joey Hess <id@joeyh.name>  Mon, 01 Nov 2021 13:19:46 -0400
 

CmdLine/GitAnnex.hs

@@ -113,6 +113,7 @@ import qualified Command.P2P
 import qualified Command.Proxy
 import qualified Command.DiffDriver
 import qualified Command.Smudge
+import qualified Command.FilterProcess
 import qualified Command.Undo
 import qualified Command.Version
 import qualified Command.RemoteDaemon
@@ -226,6 +227,7 @@ cmds testoptparser testrunner mkbenchmarkgenerator = map addGitAnnexGlobalOption
 	, Command.Proxy.cmd
 	, Command.DiffDriver.cmd
 	, Command.Smudge.cmd
+	, Command.FilterProcess.cmd
 	, Command.Undo.cmd
 	, Command.Version.cmd
 	, Command.RemoteDaemon.cmd

Command/FilterProcess.hs

@@ -0,0 +1,89 @@
+{- git-annex command
+ -
+ - Copyright 2021 Joey Hess <id@joeyh.name>
+ -
+ - Licensed under the GNU AGPL version 3 or higher.
+ -}
+
+module Command.FilterProcess where
+
+import Command
+import qualified Command.Smudge
+import Git.FilterProcess
+import Git.PktLine
+import Annex.Link
+
+import qualified Data.ByteString as B
+import qualified Data.ByteString.Lazy as L
+
+cmd :: Command
+cmd = noCommit $ noMessages $
+	command "filter-process" SectionPlumbing 
+		"long running git filter process"
+		paramNothing (withParams seek)
+
+seek :: CmdParams -> CommandSeek
+seek _ = liftIO longRunningFilterProcessHandshake >>= \case
+	Left err -> giveup err
+	Right () -> go
+  where
+	go = liftIO getFilterRequest >>= \case
+		Just (Smudge f) -> do
+			smudge f
+			go
+		Just (Clean f) -> do
+			clean f
+			go
+		Nothing -> return ()
+
+smudge :: FilePath -> Annex ()
+smudge file = do
+	{- The whole git file content is necessarily buffered in memory,
+	 - because we have to consume everything git is sending before
+	 - we can respond to it. An annexed file will be only a pointer
+	 - though. -}
+	b <- B.concat . map pktLineToByteString <$> liftIO readUntilFlushPkt
+	Command.Smudge.smudge' file (L.fromStrict b)
+	{- Git expects us to output the content of unlocked annexed files,
+	 - but if we got a pointer, we output only the pointer.
+	 - See Command.Smudge.smudge for details of how this works. -}
+	liftIO $ respondFilterRequest b
+
+clean :: FilePath -> Annex ()
+clean file = do
+	{- We have to consume everything git is sending before we can
+	 - respond to it. But it can be an arbitrarily large file,
+	 - which is being added to the annex, and we do not want to buffer
+	 - all that in memory. 
+	 -
+	 - Start by reading enough to determine if the file is an annex
+	 - pointer.
+	 -}
+	let conv b l = (B.concat (map pktLineToByteString l), b)
+	(b, readcomplete) <- 
+		either (conv False) (conv True)
+			<$> liftIO (readUntilFlushPktOrSize unpaddedMaxPointerSz)
+	
+	let passthrough
+		| readcomplete = liftIO $ respondFilterRequest b
+		| otherwise = liftIO $ do
+			-- Have to buffer the file content in memory here,
+			-- but it's not an annexed file, so not typically
+			-- large, and it's all stored in git, which also
+			-- buffers files in memory.
+			b' <- B.concat . (map pktLineToByteString)
+				<$> readUntilFlushPkt
+			respondFilterRequest (b <> b')
+	let discardreststdin
+		| readcomplete = return ()
+		| otherwise = liftIO discardUntilFlushPkt
+	let emitpointer = liftIO . respondFilterRequest . formatPointer
+	-- This does not incrementally hash, so both git and git-annex
+	-- read from the file. It may be less expensive to incrementally
+	-- hash the content provided by git, but Backend does not currently
+	-- have an interface to do so.
+	Command.Smudge.clean' (toRawFilePath file)
+		(parseLinkTargetOrPointer b)
+		passthrough
+		discardreststdin
+		emitpointer

Command/Smudge.hs

@@ -74,14 +74,18 @@ seek UpdateOption = commandAction update
 smudge :: FilePath -> CommandStart
 smudge file = do
 	b <- liftIO $ L.hGetContents stdin
-	case parseLinkTargetOrPointerLazy b of
+	smudge' file b
+	liftIO $ L.putStr b
+	stop
+
+-- Handles everything except the IO of the file content.
+smudge' :: FilePath -> L.ByteString -> Annex ()
+smudge' file b = case parseLinkTargetOrPointerLazy b of
 	Nothing -> noop
 	Just k -> do
 		topfile <- inRepo (toTopFilePath (toRawFilePath file))
 		Database.Keys.addAssociatedFile k topfile
 		void $ smudgeLog k topfile
-	liftIO $ L.putStr b
-	stop
 
 -- Clean filter is fed file content on stdin, decides if a file
 -- should be stored in the annex, and outputs a pointer to its
@@ -90,50 +94,72 @@ clean :: RawFilePath -> CommandStart
 clean file = do
 	Annex.BranchState.disableUpdate -- optimisation
 	b <- liftIO $ L.hGetContents stdin
-	ifM fileoutsiderepo
+	let passthrough = liftIO $ L.hPut stdout b
-		( liftIO $ L.hPut stdout b
+	-- Before git 2.5, failing to consume all stdin here would
-		, do
+	-- cause a SIGPIPE and crash it.
-			-- Avoid a potential deadlock.
+	-- Newer git catches the signal and stops sending, which is
-			Annex.changeState $ \s -> s
+	-- much faster. (Also, git seems to forget to free memory
-				{ Annex.insmudgecleanfilter = True }
+	-- when sending the file, so the less we let it send, the
-			go b
+	-- less memory it will waste.)
-		)
+	let discardreststdin = if Git.BuildVersion.older "2.5"
+		then L.length b `seq` return ()
+		else liftIO $ hClose stdin
+	let emitpointer = liftIO . S.hPut stdout . formatPointer
+	clean' file (parseLinkTargetOrPointerLazy b)
+		passthrough
+		discardreststdin
+		emitpointer
 	stop
   where
-	go b = case parseLinkTargetOrPointerLazy b of
+
+-- Handles everything except the IO of the file content.
+clean'
+	:: RawFilePath
+	-> Maybe Key
+	-- ^ If the content provided by git is an annex pointer,
+	-- this is the key it points to.
+	-> Annex ()
+	-- ^ passthrough: Feed the content provided by git back out to git.
+	-> Annex ()
+	-- ^ discardreststdin: Called when passthrough will not be called,
+	-- this has to take care of reading the content provided by git, or
+	-- otherwise dealing with it.
+	-> (Key -> Annex ())
+	-- ^ emitpointer: Emit a pointer file for the key.
+	-> Annex ()
+clean' file mk passthrough discardreststdin emitpointer =
+	ifM (fileOutsideRepo file)
+		( passthrough
+		, inSmudgeCleanFilter go
+		)
+  where
+
+	go = case mk of
 		Just k -> do
 			addingExistingLink file k $ do
 				getMoveRaceRecovery k file
-				liftIO $ L.hPut stdout b
+				passthrough
 		Nothing -> inRepo (Git.Ref.fileRef file) >>= \case
 			Just fileref -> do
 				indexmeta <- catObjectMetaData fileref
 				oldkey <- case indexmeta of
 					Just (_, sz, _) -> catKey' fileref sz
 					Nothing -> return Nothing
-				go' b indexmeta oldkey
+				go' indexmeta oldkey
-			Nothing -> liftIO $ L.hPut stdout b
+			Nothing -> passthrough
-	go' b indexmeta oldkey = ifM (shouldAnnex file indexmeta oldkey)
+	go' indexmeta oldkey = ifM (shouldAnnex file indexmeta oldkey)
 		( do
-			-- Before git 2.5, failing to consume all stdin here
+			discardreststdin
-			-- would cause a SIGPIPE and crash it.
-			-- Newer git catches the signal and stops sending,
-			-- which is much faster. (Also, git seems to forget
-			-- to free memory when sending the file, so the
-			-- less we let it send, the less memory it will waste.)
-			if Git.BuildVersion.older "2.5"
-				then L.length b `seq` return ()
-				else liftIO $ hClose stdin
 
 			-- Optimization for the case when the file is already
 			-- annexed and is unmodified.
 			case oldkey of
 				Nothing -> doingest Nothing
 				Just ko -> ifM (isUnmodifiedCheap ko file)
-					( liftIO $ emitPointer ko
+					( emitpointer ko
 					, updateingest ko
 					)
-		, liftIO $ L.hPut stdout b
+		, passthrough
 		)
 	
 	-- Use the same backend that was used before, when possible.
@@ -150,7 +176,7 @@ clean file = do
 		-- Can't restage associated files because git add
 		-- runs this and has the index locked.
 		let norestage = Restage False
-		liftIO . emitPointer
+		emitpointer
 			=<< postingest
 			=<< (\ld -> ingest' preferredbackend nullMeterUpdate ld Nothing norestage)
 			=<< lockDown cfg (fromRawFilePath file)
@@ -168,11 +194,21 @@ clean file = do
 
 -- git diff can run the clean filter on files outside the
 -- repository; can't annex those
-	fileoutsiderepo = do
+fileOutsideRepo :: RawFilePath -> Annex Bool
+fileOutsideRepo file = do
         repopath <- liftIO . absPath =<< fromRepo Git.repoPath
 	filepath <- liftIO $ absPath file
 	return $ not $ dirContains repopath filepath
 
+-- Avoid a potential deadlock.
+inSmudgeCleanFilter :: Annex a -> Annex a
+inSmudgeCleanFilter = bracket setup cleanup . const
+  where
+	setup = Annex.changeState $ \s -> s
+		{ Annex.insmudgecleanfilter = True }
+	cleanup () = Annex.changeState $ \s -> s
+		{ Annex.insmudgecleanfilter = False }
+
 -- If annex.largefiles is configured (and not disabled by annex.gitaddtoannex
 -- being set to false), matching files are added to the annex and the rest to
 -- git.
@@ -245,9 +281,6 @@ shouldAnnex file indexmeta moldkey = do
 			_ -> cont
 		_ -> cont
 
-emitPointer :: Key -> IO ()
-emitPointer = S.putStr . formatPointer
-
 -- Recover from a previous race between eg git mv and git-annex get.
 -- That could result in the file remaining a pointer file, while
 -- its content is present in the annex. Populate the pointer file.

Git/FilterProcess.hs

@@ -15,17 +15,18 @@ module Git.FilterProcess (
 	Version(..),
 	Capability(..),
 	readUntilFlushPkt,
+	readUntilFlushPktOrSize,
 	discardUntilFlushPkt,
 	longRunningProcessHandshake,
 	longRunningFilterProcessHandshake,
 	FilterRequest(..),
 	getFilterRequest,
+	respondFilterRequest,
 ) where
 
 import Common
 import Git.PktLine
 
-import System.IO
 import qualified Data.ByteString as B
 
 {- This is a message like "git-filter-client" or "git-filter-server" -}
@@ -85,6 +86,24 @@ readUntilFlushPkt = go []
 		Just pktline | not (isFlushPkt pktline) -> go (pktline:l)
 		_ -> return (reverse l)
 
+{- Reads PktLines until at least the specified number of bytes have been
+ - read, or until a flushPkt (or EOF). Returns Right if it did read a
+ - flushPkt/EOF, and Left if there is still content leftover that needs to
+ - be read. -}
+readUntilFlushPktOrSize :: Int -> IO (Either [PktLine] [PktLine])
+readUntilFlushPktOrSize = go []
+  where
+	go l n = readPktLine stdin >>= \case
+		Just pktline
+			| isFlushPkt pktline -> return (Right (reverse l))
+			| otherwise -> 
+				let len = B.length (pktLineToByteString pktline)
+				    n' = n - len
+				in if n' <= 0
+					then return (Left (reverse (pktline:l)))
+					else go (pktline:l) n'
+		Nothing -> return (Right (reverse l))
+
 {- Reads PktLines until a flushPkt (or EOF), and throws them away. -}
 discardUntilFlushPkt :: IO ()
 discardUntilFlushPkt = readPktLine stdin >>= \case

Git/PktLine.hs

@@ -101,9 +101,14 @@ writePktLine h (PktLine b)
 		hFlush h
 
 {- Maximum possible length of the string encoded in PktLine;
- - the length header takes up 4 bytes. -}
+ - the length header takes up 4 bytes.
+ -
+ - While the 4 byte length header can express lengths up to 65535,
+ - git actually does not support packets larger than 65520 (including the
+ - header). See "LARGE_PACKET_MAX" in the git source code.
+ -}
 maxPktLineLength :: Int
-maxPktLineLength = 65535 - 4
+maxPktLineLength = 65520 - 4
 
 flushPkt :: PktLine
 flushPkt = PktLine mempty

doc/git-annex-filter-process.mdwn

@@ -0,0 +1,48 @@
+# NAME
+
+git-annex filter-process - long running git filter process for git-annex
+
+# SYNOPSIS
+
+git annex filter-process
+
+# DESCRIPTION
+
+By default, `git-annex smudge` is used as the git filter driver.
+This is an alternative way to accomplish the same thing, using git's
+long-running filter process interface.
+
+To enable using this, run:
+
+	git config filter.annex.process 'git-annex filter-process'
+
+There will be no visible difference in behavior between enabling this and
+not, besides changes in speed and memory use when using git.
+
+When this is not enabled, each file that git wants to filter involves
+starting up a new `git-annex smudge` process. Starting many such processes
+for many files can be slow, and can make commands like `git checkout` and
+`git add` slow when they are operating on a lot of files. (A lot of locked
+annexed files do not make `git checkout` slow, but unlocked files and
+non-annexed files do slow it down.)
+
+On the other hand when this is enabled, `git add` of a large file does an
+unncessary extra read of the file, and pipes its contents into git-annex.
+So if you enable this, it will be faster to use `git-annex add` to add
+large files to the annex, rather than `git add`. Other commands that
+add files, like `git commit -a`, are also impacted by this.
+
+# OPTIONS
+
+* The [[git-annex-common-options]](1) can be used.
+
+# SEE ALSO
+
+[[git-annex]](1)
+[[git-annex-smudge]](1)
+
+# AUTHOR
+
+Joey Hess <id@joeyh.name>
+
+Warning: Automatically converted into a man page by mdwn2man. Edit with care.

doc/git-annex-smudge.mdwn

@@ -58,6 +58,7 @@ tree.
 # SEE ALSO
 
 [[git-annex]](1)
+[[git-annex-filter-process]](1)
 
 # AUTHOR
 

doc/git-annex.mdwn

@@ -713,6 +713,13 @@ content from the key-value store.
 
   See [[git-annex-smudge]](1) for details.
 
+* `filter-process`
+
+  An alternative implementation of a git filter driver, that is faster
+  in some situations and slower in others than `git-annex smudge`.
+
+  See [[git-annex-filter-process]](1) for details.
+
 * `findref [ref]`
 
   Lists files in a git ref. (deprecated)

git-annex.cabal

@@ -745,6 +745,7 @@ Executable git-annex
     Command.Expire
     Command.Export
     Command.FilterBranch
+    Command.FilterProcess
     Command.Find
     Command.FindRef
     Command.Fix
@@ -871,6 +872,7 @@ Executable git-annex
     Git.FileMode
     Git.FilePath
     Git.Filename
+    Git.FilterProcess
     Git.Fsck
     Git.GCrypt
     Git.HashObject
@@ -882,6 +884,7 @@ Executable git-annex
     Git.LsTree
     Git.Merge
     Git.Objects
+    Git.PktLine
     Git.Queue
     Git.Ref
     Git.RefLog