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I am planning to use flashcache for a filesystem, on which there is a regular cron job for making backups. For simplicity sake, let's say I am using writearound tactic and the backup job just reads... dealing with writes is another topic and I am not interested in it right now (let's say, writes are remote, for example). Do I presume correctly, that there would be no need for setting DIRECT_IO in this case and blacklist PID would work as intended?
Now the real kicker is that I am using cPanel backup procedure, that executes other processes to do the actual work (including running gtar command). How do I effectively blacklist a process tree to stop all these processes from rewriting the cache, effectively nullifying the flashcache effect (the backup procedure reads a larger amount of data than could fit onto SSD)?
I understand that theoretically I could make a wrapper for gtar and other disk-intensive processes, that would register the particular process in blacklist, and then exec the real binary (and also make a cron job to cleanup)... but that would be a horribly dirty hack. I do hope that there is a better way...
Thanks for your time,
the main problem with this approach is that the backup script is within an openvz container, so I need to make some kind of pipe or other similar way to deliver backup process pids to the host... this is very very dirty :( would it be a significant performance penalty for flashcache to check parent pid?
so if i want to have a process group id checked there (which is probably safer that just parent id in case backup job spawns plenty of processes) i would add something like this:
dontcache = flashcache_find_pid_locked(dmc, get_task_pid(current, PIDTYPE_PGID), FLASHCACHE_BLACKLIST);
somewhere in flashcache_uncacheable() ?
what are the chances that you would include this in the official version if i will give you a working patch?