On 03/06/2013 01:34 PM, Li Haifeng wrote:
2013/2/20 Ric Mason <ric.masonn@xxxxxxxxx>:
Hi Hugh,
On 02/20/2013 02:56 AM, Hugh Dickins wrote:
On Tue, 19 Feb 2013, Ric Mason wrote:
There is a call of try_to_free_swap in function swap_writepage, if
swap_writepage is call from shrink_page_list path, PageSwapCache(page) ==
trure, PageWriteback(page) maybe false, page_swapcount(page) == 0, then
will
delete the page from swap cache and free swap slot, where I miss?
That's correct. PageWriteback is sure to be false there. page_swapcount
usually won't be 0 there, but sometimes it will be, and in that case we
do want to delete from swap cache and free the swap slot.
1) If PageSwapCache(page) == true, PageWriteback(page) == false,
page_swapcount(page) == 0 in swap_writepage(shrink_page_list path), then
will delete the page from swap cache and free swap slot, in function
swap_writepage:
if (try_to_free_swap(page)) {
unlock_page(page);
goto out;
}
writeback will not execute, that's wrong. Where I miss?
when the page is deleted from swap cache and corresponding swap slot
is free, the page is set dirty. The dirty page won't be reclaimed. It
is not wrong.
I don't think so. For dirty pages, there are two steps: 1)writeback
2)reclaim. Since PageSwapCache(page) == true && PageWriteback(page) ==
false && page_swapcount(page) == 0 in swap_writeback(),
try_to_free_swap() will return true and writeback will be skip. Then how
can step one be executed?
corresponding path lists as below.
when swap_writepage() is called by pageout() in shrink_page_list().
pageout() will return PAGE_SUCCESS. For PAGE_SUCCESS, when
PageDirty(page) is true, this reclaiming page will be keeped in the
inactive LRU list.
shrink_page_list()
{
...
904 switch (pageout(page, mapping, sc)) {
905 case PAGE_KEEP:
906 nr_congested++;
907 goto keep_locked;
908 case PAGE_ACTIVATE:
909 goto activate_locked;
910 case PAGE_SUCCESS:
911 if (PageWriteback(page))
912 goto keep_lumpy;
913 if (PageDirty(page))
914 goto keep;
...}
2) In the function pageout, page will be set PG_Reclaim flag, since this
flag is set, end_swap_bio_write->end_page_writeback:
if (TestClearPageReclaim(page))
rotate_reclaimable_page(page);
it means that page will be add to the tail of lru list, page is clean
anonymous page this time and will be reclaim to buddy system soon, correct?
correct
If is correct, what is the meaning of rotate here?
Rotating here is to add the page to the tail of inactive LRU list. So
this page will be reclaimed ASAP while reclaiming.
Hugh
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