Does anyone know how to implement it ? Is there native/efficient way to manage this ?

(I'm very interested by this feature and can help to the PR)

I think it should be part of FileProfilerStorage (I would not add an interface for that for now as we don't want to support more than one storage anyway).

Instead of a max number of profiles, I would remove the oldest ones, which could be done during a call to write.
I would not make it configurable, though. Profiles are ephemeral by nature. The number of days is debatable, but I don't see any cases where you would have to have a look at a profiler older than a day, to be honest. So, let's say 2 days? Maybe 3 max?

Can we use https://symfony.com/doc/current/reference/events.html#kernel-terminate ?
Defining a DevEvent if the config is present, event responsible to purge old profiles > max_retention_days

Given such config:

framework:
  profiler:
    max_retention_days: 3 # number of days to keep local profile files

I think we can implements same logic of monolog RotatingFileHandler in FileProfilerStorage

Have a parameter in config is a good thing

I would keep this as simple as possible, aka not configurable.
Keeping just one day of profiles seems more than enough to me.

@fabpot
So when we write a new profile, we want cleaning index file and profiles files.
My approach is to read index file while we have profiles "expired". I assume it's sorted and oldest profile is on firstline.

Is it a good approach ? And cpu/memory efficient implementation ? (seems good when no expired profile, tmp file in other case)

public function removeOldestProfiles(string $indexFilename)
{
$minimalProfileTime = (new \DateTime())
    ->modify(sprintf('-%d days', self::MAX_RETENTION_DAYS))
    ->getTimestamp();

$handle = fopen($indexFilename, 'r');

$tmpIndexFileName = $indexFilename.'.tmp';
$beforeTime = true;
$atLeastOneProfileBeforeTime = false;
while ($beforeTime && $line = fgets($handle)) {
    $csv = str_getcsv($line);
    $profileTime = (int) $csv[4];

    if ($profileTime > $minimalProfileTime) {
        $beforeTime = false;
        file_put_contents($tmpIndexFileName, $line);
    } else {
        $atLeastOneProfileBeforeTime = true;
    }
}

if ($atLeastOneProfileBeforeTime) {
    file_put_contents($tmpIndexFileName, stream_get_contents($handle), FILE_APPEND);
    unlink($indexFilename);
    rename($tmpIndexFileName, $indexFilename);
} else {
    fclose($handle);
}

I can open draft PR if it a better place for theses questions