From 95f45541e47253610ed83b064dab2124a11027e8 Mon Sep 17 00:00:00 2001 From: Jin Dong Date: Fri, 3 Jan 2025 03:29:08 +0000 Subject: [PATCH] Avoid duplicated chain ID calculation in unpack This PR optimizes the chain ID calculation in unpack so we only (pre-)calculate the chain ID for layer_i exactly once, by calling `identity.ChainIDs(diffIDs)`. Currently in `unpack` for every layer_i, we calculate the chain id of layer_i-1 and layer_i *repeatedly*. Because each `identity.ChainID(diffIDs)` call involves: 1. Copy `diffIDs` to a new slice 2. Calculate chain ID for every index (by calling `ChainIDs(diffIDs)`) 3. Return the final one as result of `identity.ChainID(diffIDs)`. This means, given an image with N layers, for every layer_i: 1. we create 2 new slices and copy the diffIDs sofar; 2. we're recalculating all chain IDs from layer_0 to layer_i-1 twice; 3. in total, the chain ID for layer_i is calculated 2 * (N - layer_i) times; Signed-off-by: Jin Dong --- core/unpack/unpacker.go | 22 +++++++++++++++------- 1 file changed, 15 insertions(+), 7 deletions(-) diff --git a/core/unpack/unpacker.go b/core/unpack/unpacker.go index 35dc4dc479..d1a1e47c0d 100644 --- a/core/unpack/unpacker.go +++ b/core/unpack/unpacker.go @@ -273,8 +273,6 @@ func (u *Unpacker) unpack( a = unpack.Applier cs = u.content - chain []digest.Digest - fetchOffset int fetchC []chan struct{} fetchErr chan error @@ -285,10 +283,17 @@ func (u *Unpacker) unpack( ctx, cancel := context.WithCancel(ctx) defer cancel() + // pre-calculate chain ids for each layer + chainIDs := make([]digest.Digest, len(diffIDs)) + copy(chainIDs, diffIDs) + chainIDs = identity.ChainIDs(chainIDs) + doUnpackFn := func(i int, desc ocispec.Descriptor) error { - parent := identity.ChainID(chain) - chain = append(chain, diffIDs[i]) - chainID := identity.ChainID(chain).String() + var parent string + if i > 0 { + parent = chainIDs[i-1].String() + } + chainID := chainIDs[i].String() unlock, err := u.lockSnChainID(ctx, chainID, unpack.SnapshotterKey) if err != nil { @@ -312,7 +317,7 @@ func (u *Unpacker) unpack( for try := 1; try <= 3; try++ { // Prepare snapshot with from parent, label as root key = fmt.Sprintf(snapshots.UnpackKeyFormat, uniquePart(), chainID) - mounts, err = sn.Prepare(ctx, key, parent.String(), opts...) + mounts, err = sn.Prepare(ctx, key, parent, opts...) if err != nil { if errdefs.IsAlreadyExists(err) { if _, err := sn.Stat(ctx, chainID); err != nil { @@ -424,7 +429,10 @@ func (u *Unpacker) unpack( }).Debug("layer unpacked") } - chainID := identity.ChainID(chain).String() + var chainID string + if len(chainIDs) > 0 { + chainID = chainIDs[len(chainIDs)-1].String() + } cinfo := content.Info{ Digest: config.Digest, Labels: map[string]string{