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aufs: optimize lots of layers case

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In case there are a big number of layers, so that mount data won't fit
into a single memory page (4096 bytes on most platforms, which is good
enough for about 40 layers, depending on how long graphdriver root path
is), we supply additional layers with O_REMOUNT, as described in aufs
documentation.

Problem is, the current implementation does that one layer at a time
(i.e. there is one mount syscall per each additional layer).

Optimize the code to supply as many layers as we can fit in one page
(basically reusing the same code as for the original mount).

Note, per aufs docs, "[a]t remount-time, the options are interpreted
in the given order, e.g. left to right" so we should be good.

Tested on an image with ~100 layers.

Before (35 syscalls):
> [pid 22756] 1556919088.686955 mount("none", "/mnt/volume_sfo2_09/docker-aufs/aufs/mnt/a86f8c9dd0ec2486293119c20b0ec026e19bbc4d51332c554f7cf05d777c9866", "aufs", 0, "br:/mnt/volume_sfo2_09/docker-au"...) = 0 <0.000504>
> [pid 22756] 1556919088.687643 mount("none", "/mnt/volume_sfo2_09/docker-aufs/aufs/mnt/a86f8c9dd0ec2486293119c20b0ec026e19bbc4d51332c554f7cf05d777c9866", 0xc000c451b0, MS_REMOUNT, "append:/mnt/volume_sfo2_09/docke"...) = 0 <0.000105>
> [pid 22756] 1556919088.687851 mount("none", "/mnt/volume_sfo2_09/docker-aufs/aufs/mnt/a86f8c9dd0ec2486293119c20b0ec026e19bbc4d51332c554f7cf05d777c9866", 0xc000c451ba, MS_REMOUNT, "append:/mnt/volume_sfo2_09/docke"...) = 0 <0.000098>
> ..... (~30 lines skipped for clarity)
> [pid 22756] 1556919088.696182 mount("none", "/mnt/volume_sfo2_09/docker-aufs/aufs/mnt/a86f8c9dd0ec2486293119c20b0ec026e19bbc4d51332c554f7cf05d777c9866", 0xc000c45310, MS_REMOUNT, "append:/mnt/volume_sfo2_09/docke"...) = 0 <0.000266>

After (2 syscalls):
> [pid 24352] 1556919361.799889 mount("none", "/mnt/volume_sfo2_09/docker-aufs/aufs/mnt/8e7ba189e347a834e99eea4ed568f95b86cec809c227516afdc7c70286ff9a20", "aufs", 0, "br:/mnt/volume_sfo2_09/docker-au"...) = 0 <0.001717>
> [pid 24352] 1556919361.801761 mount("none", "/mnt/volume_sfo2_09/docker-aufs/aufs/mnt/8e7ba189e347a834e99eea4ed568f95b86cec809c227516afdc7c70286ff9a20", 0xc000dbecb0, MS_REMOUNT, "append:/mnt/volume_sfo2_09/docke"...) = 0 <0.001358>

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
This commit is contained in:
Kir Kolyshkin 2019-04-23 02:18:17 +00:00
parent 5cd62852fa
commit d58c434bff
1 changed files with 10 additions and 3 deletions
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13
daemon/graphdriver/aufs/aufs.go
View file

@ -634,9 +634,16 @@ func (a *Driver) aufsMount(ro []string, rw, target, mountLabel string) (err erro
return
}
for ; index < len(ro); index++ {
layer := fmt.Sprintf(":%s=ro+wh", ro[index])
data := label.FormatMountLabel(fmt.Sprintf("append%s", layer), mountLabel)
for index < len(ro) {
bp = 0
for ; index < len(ro); index++ {
layer := fmt.Sprintf("append:%s=ro+wh,", ro[index])
if bp+len(layer) > len(b) {
break
}
bp += copy(b[bp:], layer)
}
data := label.FormatMountLabel(string(b[:bp]), mountLabel)
a.mntL.Lock()
err = unix.Mount("none", target, "aufs", unix.MS_REMOUNT, data)
a.mntL.Unlock()