[lkml]   [2012]   [Jun]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
On 06/01/2012 01:17 PM, KOSAKI Motohiro wrote:
> Hi John,
> (6/1/12 2:29 PM), John Stultz wrote:
>> functionality for tmpfs making use of the volatile range
>> management code.
>> Conceptually, FALLOC_FL_MARK_VOLATILE is like a delayed
>> FALLOC_FL_PUNCH_HOLE. This allows applications that have
>> data caches that can be re-created to tell the kernel that
>> some memory contains data that is useful in the future, but
>> can be recreated if needed, so if the kernel needs, it can
>> zap the memory without having to swap it out.
>> In use, applications use FALLOC_FL_MARK_VOLATILE to mark
>> page ranges as volatile when they are not in use. Then later
>> if they wants to reuse the data, they use
>> FALLOC_FL_UNMARK_VOLATILE, which will return an error if the
>> data has been purged.
>> This is very much influenced by the Android Ashmem interface by
>> Robert Love so credits to him and the Android developers.
>> In many cases the code& logic come directly from the ashmem patch.
>> The intent of this patch is to allow for ashmem-like behavior, but
>> embeds the idea a little deeper into the VM code.
>> This is a reworked version of the fadvise volatile idea submitted
>> earlier to the list. Thanks to Dave Chinner for suggesting to
>> rework the idea in this fashion. Also thanks to Dmitry Adamushko
>> for continued review and bug reporting, and Dave Hansen for
>> help with the original design and mentoring me in the VM code.
> I like this patch concept. This is cleaner than userland
> notification quirk. But I don't like you use shrinker. Because of,
> after applying this patch, normal page reclaim path can still make
> swap out. this is undesirable.
Any recommendations for alternative approaches? What should I be hooking
into in order to get notified that tmpfs should drop volatile pages?

>> +static
>> +int shmem_volatile_shrink(struct shrinker *ignored, struct shrink_control *sc)
>> +{
>> + s64 nr_to_scan = sc->nr_to_scan;
>> + const gfp_t gfp_mask = sc->gfp_mask;
>> + struct address_space *mapping;
>> + loff_t start, end;
>> + int ret;
>> + s64 page_count;
>> +
>> + if (nr_to_scan&& !(gfp_mask& __GFP_FS))
>> + return -1;
>> +
>> + volatile_range_lock(&shmem_volatile_head);
>> + page_count = volatile_range_lru_size(&shmem_volatile_head);
>> + if (!nr_to_scan)
>> + goto out;
>> +
>> + do {
>> + ret = volatile_ranges_get_last_used(&shmem_volatile_head,
>> + &mapping,&start,&end);
> Why drop last used region? Not recently used region is better?
Sorry, that function name isn't very good. It does return the
least-recently-used range, or more specifically: the

I'll improve that function name, but if I misunderstood you and you have
a different suggestion for the purging order, let me know.


 \ /
  Last update: 2012-06-01 23:21    [W:0.356 / U:0.744 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site