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Minor SGV docs improvements

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git-svn-id: http://svn.code.sf.net/p/scst/svn/trunk@1064 d57e44dd-8a1f-0410-8b47-8ef2f437770f
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Vladislav Bolkhovitin
2009-09-02 09:58:31 +00:00
parent 0785ab7746
commit 56440d9262
1 changed files with 15 additions and 9 deletions
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doc/sgv_cache.txt
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@@ -7,15 +7,21 @@
SCST SGV cache is a memory management subsystem in SCST. One can call it
a "memory pool", but Linux kernel already have a mempool interface,
which serves different purposes. SGV cache provides to SCST core, target
drivers and backend dev handlers facilities to allocate and build SG
vectors for data buffers. The main advantage of it is that it doesn't
free to the system each vector, which is not used anymore, but keeps it
for a while to let it be reused by the next consecutive command. This
allows to reduce commands processing latency and, hence, improve
performance. The freed SG vectors are kept by the SGV cache either for
some predefined time, or until the system needs more memory and asks to
free some using the set_shrinker() interface. Also the SGV cache allows
to:
drivers and backend dev handlers facilities to allocate, build and cache
SG vectors for data buffers. The main advantage of it is the caching
facility, when it doesn't free to the system each vector, which is not
used anymore, but keeps it for a while (possibly indefinitely) to let it
be reused by the next consecutive command. This allows to:
- Reduce commands processing latencies and, hence, improve performance;
- Make commands processing latencies predictable, which is essential
for RT applications.
The freed SG vectors are kept by the SGV cache either for some (possibly
indefinite) time, or, optionally, until the system needs more memory and
asks to free some using the set_shrinker() interface. Also the SGV cache
allows to:
- Cluster pages together. "Cluster" means merging adjacent pages in a
single SG entry. It allows to have less SG entries in the resulting SG