svn commit: r309017 - in head/sys: cddl/compat/opensolaris/sys compat/linprocfs fs/tmpfs sys vm

[Alan Cox]

On 03/03/2018 02:48, Alexey Dokuchaev wrote:
> On Tue, Nov 22, 2016 at 06:13:46PM +0000, Alan Cox wrote:
>> New Revision: 309017
>> URL: https://svnweb.freebsd.org/changeset/base/309017
>>
>> Log:
>>   Remove PG_CACHED-related fields from struct vmmeter, because they are no
>>   longer used.  More precisely, they are always zero because the code that
>>   decremented and incremented them no longer exists.
>>   
>>   Bump __FreeBSD_version to mark this change.
>>   
>>   Reviewed by:	kib, markj
>>   Sponsored by:	Dell EMC Isilon
>>   Differential Revision:	https://reviews.freebsd.org/D8583
>>
>> Modified: head/sys/cddl/compat/opensolaris/sys/kmem.h
>> ...
>> -#define	freemem				(vm_cnt.v_free_count + vm_cnt.v_cache_count)
>> +#define	freemem				vm_cnt.v_free_count
> This looks correct now.
>
>> Modified: head/sys/compat/linprocfs/linprocfs.c
>> ...
>> @@ -176,7 +176,7 @@ linprocfs_domeminfo(PFS_FILL_ARGS)
>>  	 * like unstaticizing it just for linprocfs's sake.
>>  	 */
>>  	buffers = 0;
>> -	cached = vm_cnt.v_cache_count * PAGE_SIZE;
>> +	cached = vm_cnt.v_inactive_count * PAGE_SIZE;
> Some applications that make calculations based on the readings from the
> /usr/compat/linux/proc/meminfo are broken after this change, e.g. those
> that do things like:
>
>     return (totalMem - (freeMem + buffers + cache)) / totalMem;
>
> because now free memory includes cached one, and above formula gives
> bogus negative result.
>
> In `sys/compat/linprocfs/linprocfs.c', memfree is calculated as follows:
>
>     memtotal = physmem * PAGE_SIZE;
>     /*
>      * The correct thing here would be:
>      *
>     memfree = vm_cnt.v_free_count * PAGE_SIZE;
>     memused = memtotal - memfree;
>      *
>      * but it might mislead linux binaries into thinking there
>      * is very little memory left, so we cheat and tell them that
>      * all memory that isn't wired down is free.
>      */
>     memused = vm_cnt.v_wire_count * PAGE_SIZE;
>     memfree = memtotal - memused;
>
> So, when vm.stats.vm.v_cache_count was yielding some (typically small)
> result, using the aforementioned trick made sense (because even when
> vm_cnt.v_free_count added to vm.stats.vm.v_cache_count it would still
> be rather small).  This logic no longer applies after this change.
>
> On my 12-CURRENT i386 system, /usr/compat/linux/proc/meminfo reports:
>
>     % cat /usr/compat/linux/proc/meminfo | head -4
>     MemTotal:   3132504 kB
>     MemFree:    2925936 kB			<<< that's a lot
>     Buffers:          0 kB
>     Cached:     2212196 kB			<<< that's also a lot
>
> On an older 4.11-STABLE box (also i386), it reports:
>
>     MemTotal:    521828 kB
>     MemFree:     383976 kB
>     MemShared:     7480 kB
>     Buffers:          0 kB
>     Cached:       22732 kB (can be added to MemFree and still < MemTotal)
>
> So either the "cheat" have to go away and vm_cnt.v_free_count used as it
> should, or cached memory should not be read from vm_cnt.v_inactive_count
> but estimated somehow else.  Which approach would be more correct?

The former.