Re: Fairness in love and swapping

Dr. Werner Fink (werner@suse.de)
Wed, 25 Feb 1998 22:39:47 +0100

>
> I noticed something rather unfortunate when starting up two of these
> tests simultaneously, each test using a bit less than total physical
> memory. The first test gobbled up the whole of ram as expected, but the
> second test did not. What happened was that the contention for memory
> was keeping swap active all the time, but the processes which were
> already all in memory just kept running at full speed and so their pages
> all remained fresh in the page age table. The newcomer processes were
> never able to keep a page in memory long enough for their age to compete
> with the old process' pages, and so I had a number of identical
> processes, half of which were fully swapped in and half of which were
> swapping madly.

Maybe my changes done for 2.0.3x in ipc/shm.c: shm_swap_in()

shm_rss++;

/* Give the physical reallocated page a bigger start */
if (shm_rss < (MAP_NR(high_memory) >> 3))
mem_map[MAP_NR(page)].age = (PAGE_INITIAL_AGE + PAGE_ADVANCE);

and mm/page_alloc.c: swap_in()


vma->vm_mm->rss++;
tsk->maj_flt++;

/* Give the physical reallocated page a bigger start */
if (vma->vm_mm->rss < (MAP_NR(high_memory) >> 2))
mem_map[MAP_NR(page)].age = (PAGE_INITIAL_AGE + PAGE_ADVANCE);

would help a bit. With this few lines a recently swapin page gets a bigger
start by increasing the page age ... but only if the corresponding process to
not overtake the physical memory. This change is not very smart (e.g. its not
a real comparsion by process swap count or priority) ... nevertheless it works
for 2.0.33.

>
> Needless to say, this is highly unfair, but I'm not sure whether there
> is any easy way round it --- any clock algorithm will have the same
> problem, unless we start implementing dynamic resident set size limits.
>

Werner

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