On Thu, May 4, 2017 at 4:36 PM, Xavier Hernandez <xhernandez@xxxxxxxxxx> wrote:
Hi,
On 30/04/17 06:03, Raghavendra Gowdappa wrote:
All,
Its a common perception that the resolution of a file having linkto file on the hashed-subvol requires two hops:
1. client to hashed-subvol.
2. client to the subvol where file actually resides.
While it is true that a fresh lookup behaves this way, the other fact that get's ignored is that fresh lookups on files are almost always prevented by readdirplus. Since readdirplus picks the dentry from the subvolume where actual file (data-file) resides, the two hop cost is most likely never witnessed by the application.
This is true for workloads that list directory contents before accessing the files, but there are other use cases that directly access the file without navigating through the file system. In this case fresh lookups are needed.
I agree, if the contents of parent directory are not listed at least once, penalty is still there.
Xavi
A word of caution is that I've not done any testing to prove this observation :).
regards,
Raghavendra
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Raghavendra G
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