https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=222356
Bug ID: 222356
Summary: www/firefox: file-backed shared memory performance
Product: Ports & Packages
Version: Latest
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: Individual Port(s)
Assignee: [email protected]
Reporter: [email protected]
CC: [email protected], [email protected]
Assignee: [email protected]
Flags: maintainer-feedback?([email protected])
Created attachment 186420
--> https://bugs.freebsd.org/bugzilla/attachment.cgi?id=186420&action=edit
firefox patch
Multi-process firefox appears to use a lot of shared memory backed by files on
/tmp. If /tmp is not tmpfs but a regular file system this causes significant
delays. Scrolling pages can be slow for example. This can be improved by
patching firefox to use MAP_NOSYNC which prevents dirty pages being flushed to
disc as long as they are mapped. When they are unmapped (and all descriptors
have been closed) FreeBSD still flushes them though and there are several
situations where firefox does this (e.g. switching between tabs and minimising
and restoring the browser window). The backing files have been unlinked so why
doesn't FreeBSD just discard the pages?
I've attached a patch for firefox that works around this problem by using POSIX
shared memory with shm_open for the case of anonymous shared memory. Named
shared memory is left unchanged but doesn't appear to be used. The patch also
removes recording of the inode because I don't think it's valid for shm_open.
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