Date: Wed, 13 Mar 2002 23:24:29 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Vladimir Dozen <vladimir-dozen@mail.ru> Cc: hackers@freebsd.org, Poul-Henning Kamp <phk@critter.freebsd.dk>, Wilko Bulte <wkb@freebie.xs4all.nl>, Alfred Perlstein <bright@mu.org> Subject: Re: VM: file swapping (this time in libc): patch Message-ID: <200203140724.g2E7OTP38934@apollo.backplane.com> References: <200109300752.f8U7qsj41649@earth.backplane.com> <909.1001839737@critter> <20011003233444.A8637@eix.do-labs.spb.ru> <20011004204023.C2422@eix.do-labs.spb.ru>
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Ok, there are two rather serious problems with this patch:
(1) When you use a MAP_PRIVATE mapping, modifications to the mapped memory
are backed by swap, not by the file. That is what MAP_PRIVATE does
by definition.
(2) You can't safely use MAP_SHARED unless you also deal with fork()
or you will share what is supposed to be process-private memory
across the fork().
-Matt
Matthew Dillon
<dillon@backplane.com>
:ehlo.
:
: I was told that diff format I used is unappropriate for most cases,
: so I redo it in unified (-u) format.
:
: Purpose: to allow developers of large applications to use system
: memory allocation routines for allocating in mmap()ed file
: instead of writing own ones. Also, allow to run applications that
: may use huge amount of memory (like Gimp) without reconfiguring
: swap.
:
: Patch description: the patch implements file-backed memory
: allocation for regular malloc() routine. If 'F' flag is set
: in malloc options, instead of doing mmap(MAP_ANON), malloc()
: maps regions from temporal file. File is growed as neccessary,
: and new regions are mapped from the same file.
:
: Details: to avoid using two methods of allocation (brk() and mmap()) in
: the same file, regular allocation altered to use mmap(). This
: is done by writing emulators (brk_emulator() and sbrk_emulator()).
: File allocator uses single descriptor (usually fd==512). File is
: created in directory specified by $SWAPDIR, $TMPDIR or "/tmp"
: (in this order). $SWAPDIR is introduced since often people use
: memory file system for /tmp. Temporal file is unlinked after
: creation, so it will be deleted automatically at exit.
:
: Informal testing shows no performance hit comparing with old-style
: brk() allocation, and small hit when using file-backed allocation.
:
: Here the patch (made on 4.3-RELEASE-p20)
:===============================
:--- malloc.c.old Tue Oct 2 12:52:25 2001
:+++ malloc.c Thu Oct 4 20:05:52 2001
:@@ -97,7 +97,7 @@
:...
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