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[tor-bugs] #11790 [Tor]: Our zlib deflate objects require lots of memory per directory connection
#11790: Our zlib deflate objects require lots of memory per directory connection
-----------------------------------------+---------------------------------
Reporter: nickm | Owner:
Type: defect | Status: new
Priority: normal | Milestone: Tor:
Component: Tor | 0.2.6.x-final
Keywords: tor-relay zlib 025-backport | Version:
Parent ID: | Actual Points:
| Points:
-----------------------------------------+---------------------------------
Compressing descriptors on the fly requires a lot of memory with zlib's
default settings. According to zconf.h:
{{{
/* The memory requirements for deflate are (in bytes):
(1 << (windowBits+2)) + (1 << (memLevel+9))
that is: 128K for windowBits=15 + 128K for memLevel = 8 (default
values)
plus a few kilobytes for small objects.
}}}
We are using windowbits == 15 and memLevel == 8. This might explain in
part why busy directories are so memory-hungry. In addition to our
investigations for #11787, we should see whether we can safely reduce this
to 32K or so with windowBits == 12 and memlevel == 5. It appears in
preliminary investigation that this compression level would not hurt
compression very much (0-5% for microdescs, 3-7% for server descriptors).
We could also choose our window size and memlevel based on current memory
availability.
--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/11790>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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