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Andrea Arcangeli: 2.2.20pre2aa1

May 15, 2001, 22:29 (0 Talkback[s])
Subject: 2.2.20pre2aa1
Date: Tue, 15 May 2001 23:58:59 +0200
From: Andrea Arcangeli <andrea@suse.de>

The main features of 2.2.20pre2aa1 are:

o       Support for 4Gigabyte of RAM on IA32 (me and Gerhard Wichert)
o       Support for 2T of RAM on alpha (me)
o       RAW-IO (doable with bigmem enabled too). Improvements are also been
        backported from 2.4.
o       SMP scheduler improvements. (me and partly from 2.3.x contributed
by Ingo Molnar)
o       LFS (>2G file on 32bit architectures) also NFSv3 works over 2G
        (nfsv3-lfs work from me, Andi and fix from Jay Weber)
o       fixed race in wake-one LIFO in accept(2). Apache must be compiled
with -DSINGLE_LISTEN_UNSERIALIZED_ACCEPT to take advantage of that.
o      lowlatency and SMP scalability in all copy-user and tcp_sendmsg
o       GFS support.
o       various fixes

Detailed description of 2.2.20pre2aa1 follows.

------ 00_4_min_percent-1

        Increase the min percent of the buffer cache and page cache to 4%.
        (it wouldn't matter if the VM algorithms were better). (me)


        Avoid suprious unplug of the I/O queue. (me)


        Allows the kernel to be compiled for K7 (AMD Athlon) or Pentium4.

        This compilations options _only_ make the kernel to assume
respectively 64byte cachelines or 128byte cachelines.

        Those assumptions are critical mostly on SMP systems, but even UP
will take advantage of it because it will make most performance
        critical slab allocations to start on a cacheline boundary.

        Since the only difference between Ppro/K7/P4 compilations
        is the cacheline size assumed by the kernel you can safely boot
        a K7/P4 compiled kernel on a Ppro, it won't obviously generate
        cacheline pinpongs in SMP. There are only two downsides in
        running on a Ppro (PII/PIII included) a K7/P4 compiled kernel:

        1)      some byte of memory wasted due the larger paddings (really not
                a big deal)
        2)      potential waste of cacheline sets. On PII and PIII and PPro
                the L1 dcache is 8kbyte or 16kbytes 2-way set associative (so
                there are 128 or 256 sets of cachelines) and by stressing the
                first 32bytes of the 128 byte aligned data structures (for
                example if the kernel is compiled for P4) you would take
                advantage of only 1/4 of the available L1 cache. (you would
                stress set 0, 4, 8, ... only) This is probably quite serious
                issue in terms of performance. So for Ppro/PII/PIII you're
                still suggested to use Ppro compilation option (if care to
                optimize the L1 cache usage).

        (me and Andi)


        Fix a local APIC initaliziation ordering bug that triggers on the


        SSE/SSE2 support (unmasked exception via mxcsr included).
        (mix of Doug Ledford, Ingo Molnar, Gabriel Paubert PIII patch for
        2.2.x and 2.4.x PIII support from Gareth Hughes, audited, fixed and
        changed by me to be dynamic. At the end it's very similar to the
        2.4.x support)

        Kernel now understands the `nofxsr' boot time parameter and it
        doesn't enable fxsr in that case (if there's any CPU that
        crashes at boot because it's buggy, nofxsr will workaround
        the hardware bug; it's also useful for asymetric multiprocessing
        where boot cpu can have fxsr capabilities and the other cpus hasn't)


        Pass the reason for the sigio in the si_code (and a duplicate info
        in si_band) with the same API of 2.4.x. This avoids people
        having to poll a set of fd during the sigio handler. (current
        2.4.x has two bugs in that area but fixes are in Linus's mailbox)


        Better SMP reschedule_idle. (partly backported from 2.3.x, 2.3.x
        version was contributed by Ingo Molnar)

        Fixes the wmb() in schedule_tail that should really be a mb(), in
        theory one of the last reads in reschedule_idle could return garbage
(in practice I think it can't trigger... at least on x86 :) (me)


        wait I/O completion as well while doing the Wait_IO second pass on
the dirty cache (should fix last VM problem reported by VA while
creating very large ext2 fs on lowmem machines)


        Allows device drivers to set the VMA as reserved to avoid swap_out
to try to unmap stuff from them (this avoid device drivers using
->nopage for lazily mapping scatter gather dma areas in userspace,
to implement a noop swapout and it also avoids useless page faults).
This is much more efficient than setting the physical pages as


        Fixes the RTC parsing done by the kernel at boot. (backported from


        Fix from Andi for the compatibility 2.4 interface (mark_bh was


        Avoid a suprious useless unplug of the I/O queue. (me)


        Additional paranoid stuff in TCP delayed acks code (if somebody
        can still reproduce lockups under heavy TCP load, the
        delack-timer-5 patch can be the solution). In 2.2.15 only what
        was obviously wrong is been fixed, but at the time I did
        delack-timer-5 I was convinced the stuff in 2.2.15 _might_ not be
        enough, so if you have still lockups under 2.2.15 let us know.
        delack-timer-5 is reported to definitely fix the TCP lockup. (me)


        Fix elevator merging when tasks blocks waiting for new requests.


        Declare rtc_lock external spinlock to fix compilation. (me)


        Make the inode-max and ihash dynamic. Mean distribution in the
        hash is of 1. inode-max remains the same until 256M of ram.
        It then reaches 32k inodes with 512Mbyte of ram and 64k inodes
        with 1G of ram and then it stops growing. It's true dcache
        avoids most of the iget when everything fits in the working set,
        but as soon there's icache pollution iget will run all the time
        so it's not true iget hash table doesn't matter for performance.

        The ihash hasnfn is very bad in both 2.2.x and 2.4.x:

                unsigned long tmp = i_ino | (unsigned long) sb;

        Think what happens if `sb' has many bits set to 1, it will generate
an huge collision chain. It should have been at least an xor, not an
or. So I changed it this way:

                unsigned long tmp = i_ino + (unsigned long) sb / (sizeof(struct
super_block) & ~(sizeof(struct super_block) - 1));

        This will shift right sb with around `super_block size' granularity
        and it will share hash cachelines if the user asks for consecutive
        inode numbers (can be the case).



        Revertd the semantic change that make differences between
        /proc/00000$$ and /proc/$$, this allows backwards compatibilty of
        a misfeature and it _won't_ hurt security. There's no downside
        in reverting the 2.2.13 semantic change.


        Allows large kupdate intervals (don't change the interval unless
        you know what you're doing!)


        Allows kupdate to be stopped via SIGSTOP (currently it must be
        stopped by setting interval to zero via sysctl). This returns
        useful in the airplane where you do killall -STOP
        kupdate... STOP kupdate at your own risk of course ;) (me)


        Instead of making a single threaded async daemon to avoid unplugging
        the queue all the time, the blockdevice code is been changed
        to allow the loop device to handle merged requests. (me)


        Avoids mremap to grow in virtual addresses (and so in turn
        it avoids to waste virtual address space).


        Provide nanosleep usec resolution so that a signal flood doesn't
        hang glibc folks that correctly trust the rem field to resume
        the nanosleep after a syscall interruption. (without the patch
        nanosleep resolution is instead 10msec on IA32 and around 1msec on
        alpha) (me)


        ext2 64bit fix


        Make sure to not understimate the available memory (the cache and
        buffers may be under the min percent) (me)


        If child exists _before_ it got the timeslice refresh parents
        gets its timeslice back. 2.4.x does that even if child got
        the refresh and it's wrong.

        This feature avoids programs like `bash scripts' to be starved while
        forking short-lived childs at high frequency.



        Don't generate suprious unplug of the queue during readahead.


        Some more info out of SYSRQ+P.


        Avoid stack to silenty overflow on the heap (make life easier
        to track down userspace issues). Perfect approch is not possible
        even using special LDT for the stack segment. The approch in the
        patch will work 99% of the time and it enforces a GAP between heap
        and stack of 1 page as default (configurable via sysctl, if
        turned to zero the feature is disabled completly). (me)


        TSC calibration must be dynamic and not a compile time thing
        because gettimeofday is dynamic and it depends on the TSCs
        to be in sync. (me)


        Change to the Makefile EXTRAVERSION.


        Backport 2.4 waitqueues and in turn fixes an hanging condition in



        Use only ordered string operations while writing to IOMMU areas.
        the non __ versions can be reordered at compile time. (Doug Ledford)


        BIGMEM production code (IA32 and alpha). This one fixes
        a memory leak during swap (almost unreproducibe, found it
        while reading the sources only) and some alpha-bigmem
        bug. It's now possible to generate core dumps larger
        than 2G (the previous limitation was due a few ext2
        bugs and a binfmt_elf.c bug that need to be fixed in 2.4.x too).
        I just includes the large_shm patch so it should be possible to
        allocate more than 2g in one shm segment. (me and Gerhard Wichert)

        Includes >4G mtrr support developed by Boszormenyi Zoltan.

        Recently fixed sysinfo structure to be defined as:

                char _f[22-3*sizeof(long)+sizeof(short)];

        so that sysinfo(2) doesn't overflow the user buffer on 64bit

        Also 2.4.x is buggy in that respect and needs to be fixed, btw.


        SCT's rawio bigmem capable. (Stephen C. Tweedie)
        Backported latest 2.4.4 improvements.


        beta4 LVM compatible with the 2.4.5pre2aa1 beta7 one. (Heinz


        Implements the consistent snapshot API so that for example we can
        live snaphost reiserfs.


        Fixes hardblocksize bug present in beta4 lvm. (me)

        (the fix is been merged in lvm beta7 btw)


        use the preallocated block array in the kiobuf to save stack. (me)


        Needed by alpha SMP. (won't be needed anymore in 2.4.x)


        LFS: >2G file support for 32bit archs. This also includes
        the new getdents64 and fcntl64 syscalls in sync with the
        2.4.x user <-> kernel API. It also fixes some bug
        present in the previous 2.2.x LFS patches. Support for
        nfsv3 is complete as well on both server and client side.


        Avoid duplicating disconnect dentries. (Chip)


        Relocate the initrd image ASAP (btw, on alpha `ASAP' happens sooner
        than on IA32 due kseg), to avoid corrupting it while allocating the
        boot memory (like the mem_map_t array). This is good for robusteness
        and it's mainly interesting when bigmem is enabled.


        Implements conditional_schedule(). (Ingo Molnar from lowlatency


        Add low latency schedule entry points into the copy_user(), this
fixes read(2)/write(2) hangs. (Originally implemented by Ingo Molnar
in the lowlatency patch, but this patch is not equivalent, it's a
very subset and it's different: the reason I put the
        conditional schedule _after_ the copy is because we want the
        higher timeslice possible once we return to userspace to avoid
        live locks during swap)


        Drop the big kernel lock during copy-user that can release
        it anyways while getting faults. Improves SMP scalability. (me)


        Drop big kernel lock during TCP checksum (in tcp_sendmsg). Receiver
        side can't drop the big lock as it doesn't have a process context.


        Same as above for alpha architecture.


        Same as above for ppc, sparc, sparc64 architectures.


        Fix implementation bugs in spinlocks and other SMP atomic operations
        that needs to declare "memory" as clobbered. Didn't removed the
        __dummy structures in 2.2.x to make sure not to trigger any compiler
        issue. (me)


        NMI wathdog is compiled in without configuration options.
        It's disabled by default. To enable it dynamically at boot
        pass the kernel the parameter "nmi_irq=0". nmi_irq=0 makes sense
        on SMP only. (original patch from Ingo Molnar, fixed to work again
in late 2.2.x kernels and made it dynamic by me)


        RAID 0.90 updates from Ingo (it needs raidtools, not mdutils)


        During reads from raid1 keep the two disks working on different
        areas of the raid1. (Mika Kuoppala)


        Add hooks in the buffer head that GFS needs.


        make scsi command length dynamic (max 16) instead of fixed to 12.
        (needed by GFS)


        export rscsi_disks structure from sd.c for GFS. Note the equivalent
        patch in GFS latest release is buggy and I had to fix it up to allow
        sd_mod to be compied correctly. (just reported to GFS folks)


        Calls lowlevel f_ops->lock also from flock (not only from
        fcntl(F_*K)). needed by GFS.


        Export a few kernel functions for GFS module. (This was buggy
        too in the GFS latest release and it's just reported and fixed here)


        Added device_names to generic disk structure (for GFS).


        Added few ioctl to sparc64 32bit ioctl wrapper for GFS.


        Export change_termios to modules (for GFS).


        Added fs_transaction field to the task structure (for GFS).


        Added generic map_fn/request_fn to ll_rw_block. The interface with
        MD and LVM got broken so it had to be fixed too. (for GFS).


        Insert the GFS inode in the inode structure.
        GFS uses same inode for named pipes/unix sockets and
        GFS itself, so left some space before putting generic_ip pointer
        in the gfs_inode_info.


        Implements hard_panic() function that will attempt to show the
message nad reboot the machine after some second.


        Pass the opaque cookie of iget4 back to the filesystem during
        the read_inode callback.


The 2.2.20pre2aa1 patch is here:


As usual all the separate patches are in:


and they can be applyed in `ls` order to generate the
2.2.20pre2aa1.bz2 kernel.

Have fun.


PS. If you'll run with more than 4giga of RAM on alpha, you'll need
also to fix procps if you want to read the correct MM values with
`free`, `top` and `vmstat`. procps takes all the memory information
with byte granularity in `int` words (and not long words). I fixed
procps this way: