reply cache
Subsystems (2)
Hi all,
According to the file fs/nfsd/nfscache.c (line 30 on 2.6.23), reply cache is fixed size. Why is this a fixed size cache? Shouldn't be relative to the number of nfsd threads? I've a server with this statistics:
rc 0 959398 336415498
By what I've been researching this means: 0 hits, 959398 misses (I supose that means something like "recently deleted") and 336415498 not in cache (and never has been). Is that right?
Modifying the CACHESIZE to a bigger size do you think it could enhance NFS performance by getting some hits on the reply cache?
Thanks!
Jordi
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Quoted 10 lines · Jordi Prats
Hi all,
According to the filefs/nfsd/nfscache.c(line 30 on 2.6.23), reply cache is fixed size. Why is this a fixed size cache? Shouldn't be relative to the number of nfsd threads? I've a server with this statistics:rc 0 959398 336415498
By what I've been researching this means: 0 hits, 959398 misses (I supose that means something like "recently deleted") and 336415498 not in cache (and never has been). Is that right?
No, the large number is NOCACHE, which means the operation does not require caching at all (it's an idempotent operation). The smaller number is either a new operation that does require caching, or a retransmit that didn't hit.
Quoted 2 lines
Modifying the CACHESIZE to a bigger size do you think it could enhance NFS performance by getting some hits on the reply cache?
A bigger cache will only waste memory in your case. If you had a very large miss count, then it might be warranted, but in any case it is not going to help performance unless you're seeing a large number of client retransmits. And even then, the fix is not a bigger cache.
Tom.
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Quoted 5 lines · Jordi Prats
According to the file
fs/nfsd/nfscache.c(line 30 on 2.6.23), reply cache is fixed size. Why is this a fixed size cache? Shouldn't be relative to the number of nfsd threads? I've a server with this statistics:rc 0 959398 336415498
By what I've been researching this means: 0 hits, 959398 misses (I supose that means something like "recently deleted") and 336415498 not in cache (and never has been). Is that right?
A DRC hit implies the client is retransmitting. Not having any hits is a good thing -- it means your server is able to handle all your clients without much sweat.
Quoted 1 line
Modifying the CACHESIZE to a bigger size do you think it could enhance NFS performance by getting some hits on the reply cache?
The server's DRC is not a performance feature. It's a way for the server to detect replayed requests from the client. In a perfect world, servers wouldn't even have one.
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Thank you!
I miss understood the reply cache, I was thinking it as a way it caches the answer to a question like "which are the attributes of that file?"
Now I'm happy with my zero hits ;)
Jordi
Quoted 16 lines · Chuck Lever
Quoted 10 lines · Jordi Prats
According to the file
fs/nfsd/nfscache.c(line 30 on 2.6.23), reply cache is fixed size. Why is this a fixed size cache? Shouldn't be relative to the number of nfsd threads? I've a server with this statistics:rc 0 959398 336415498
By what I've been researching this means: 0 hits, 959398 misses (I supose that means something like "recently deleted") and 336415498 not in cache (and never has been). Is that right?
A DRC hit implies the client is retransmitting. Not having any hits is a good thing -- it means your server is able to handle all your clients without much sweat.
Quoted 6 lines
Quoted 2 lines
Modifying the CACHESIZE to a bigger size do you think it could enhance NFS performance by getting some hits on the reply cache?
The server's DRC is not a performance feature. It's a way for the server to detect replayed requests from the client. In a perfect world, servers wouldn't even have one.
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