On Tue, Apr 09, 2013 at 01:36:52PM +0800, Ric Mason wrote: > Hi Minchan, > On 04/09/2013 09:02 AM, Minchan Kim wrote: > >Hi Andrew, > > > >On Mon, Apr 08, 2013 at 02:17:10PM -0700, Andrew Morton wrote: > >>On Mon, 8 Apr 2013 15:01:02 +0900 Minchan Kim <minchan@xxxxxxxxxx> wrote: > >> > >>>Swap subsystem does lazy swap slot free with expecting the page > >>>would be swapped out again so we can avoid unnecessary write. > >>Is that correct? How can it save a write? > >Correct. > > > >The add_to_swap makes the page dirty and we must pageout only if the page is > >dirty. If a anon page is already charged into swapcache, we skip writeout > >the page in shrink_page_list, then just remove the page from swapcache and > >free it by __remove_mapping. > > > >I did received same question multiple time so it would be good idea to > >write down it in vmscan.c somewhere. > > > >>>But the problem in in-memory swap(ex, zram) is that it consumes > >>>memory space until vm_swap_full(ie, used half of all of swap device) > >>>condition meet. It could be bad if we use multiple swap device, > >>>small in-memory swap and big storage swap or in-memory swap alone. > >>> > >>>This patch makes swap subsystem free swap slot as soon as swap-read > >>>is completed and make the swapcache page dirty so the page should > >>>be written out the swap device to reclaim it. > >>>It means we never lose it. > >>>From my reading of the patch, that isn't how it works? It changed > >>end_swap_bio_read() to call zram_slot_free_notify(), which appears to > >>free the underlying compressed page. I have a feeling I'm hopelessly > >>confused. > >You understand right totally. > >Selecting swap slot in my description was totally miss. > >Need to rewrite the description. > > free the swap slot and free compress page is the same, isn't it? I think so. I just wanted to make my description more clear with more general terms. :) Thanks. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>