overlay: try harder with more layers #1375
Conversation
nalind
force-pushed
the
overlay-harder
branch
5 times, most recently
from
00eb305
to
94f8d8e
Compare
nalind
force-pushed
the
overlay-harder
branch
from
94f8d8e
to
59d3fb8
Compare
|
This is making me consider if we'd just be better off recording layer IDs in "${layer}/lower" in "${layer}/diff" form and dispensing with the symbolic link farm in "l" entirely. We'd fork/exec for mounting a lot more often. |
drivers/overlay/mount.go
Outdated
| // paths, but we don't want to mess with other options. | ||
| var upper, work, lower, label, other string | ||
| for _, arg := range strings.Split(options.Label, ",") { | ||
| if strings.HasPrefix(arg, "upperdir=") { |
There was a problem hiding this comment.
Style only:
nv := strings.SplitN(arg, "=")
switch nv[0] {
case "upperdir":
upper = nv[1]
…
}(and eventually strings.Cut with Go 1.18.)
Separately: The caller has all of this data. It feels a bit tedious to format it into a single string, and then parse it out again — but changing that would be a rather larger rewrite.
drivers/overlay/mount.go
Outdated
|
|
||
| // Reconstruct the Label field. | ||
| options.Label = "" | ||
| for _, arg := range []string{upper, work, lower, label, other} { |
There was a problem hiding this comment.
[A] …
something like
for _, pair := range []struct{optionName, value string} {
{ "upperdir=", upper },
…
{ "", other },
}would allow most of this function to only deal with the individual values instead of the mount syntax.
(Ultimately, this “turn option values into a mount option syntax string” code might be useful to completely factor out…)
If we have enough layers that even using relative paths for symlinks to the diff directories won't make the list of lower directories and options fit in a single page, * open the various lowers for reading * use the descriptor names in the lowerdir= list This is a bit slower, so don't take these extra steps unless we know we have to. Signed-off-by: Nalin Dahyabhai <nalin@redhat.com>
nalind
force-pushed
the
overlay-harder
branch
from
59d3fb8
to
7c5964d
Compare
|
@mtrmac PTAL again. |
| // is true (512 is a buffer for label metadata). | ||
| // is true (512 is a buffer for label metadata, 128 is the | ||
| // number of lowers we want to be able to use without having | ||
| // to use bind mounts to get all the way to the kernel limit). | ||
| // ((idLength + len(linkDir) + 1) * maxDepth) <= (pageSize - 512) |
There was a problem hiding this comment.
Now the inequality does not hold. s/maxDepth/128/ or maybe … maxDirect = 128 is the … and * maxDirect?
There was a problem hiding this comment.
Opened #1392 to do the first one.
If we have enough layers that even using relative paths for symlinks to the diff directories won't make the list of lower directories and options fit in a single page,
create a temporary directorymount a tmpfs therebind mount from the diff directories to subdirectories of the temp directory with short namesmount using those bind-mounted directories as the lower directoriesdetach the temporary directoryremove the temporary directorylowerdir=listThis is
noticeablyslower, so don't take these extra steps unless we know we absolutely have to.Should help with cri-o/cri-o#6261.