On Mon, 8 Mar 2010 11:17:24 +0900
Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx> wrote:
> > But IIRC, clear_writeback is done under treelock.... No ?
> >
> The place where NR_WRITEBACK is updated is out of tree_lock.
>
> 1311 int test_clear_page_writeback(struct page *page)
> 1312 {
> 1313 struct address_space *mapping = page_mapping(page);
> 1314 int ret;
> 1315
> 1316 if (mapping) {
> 1317 struct backing_dev_info *bdi = mapping->backing_dev_info;
> 1318 unsigned long flags;
> 1319
> 1320 spin_lock_irqsave(&mapping->tree_lock, flags);
> 1321 ret = TestClearPageWriteback(page);
> 1322 if (ret) {
> 1323 radix_tree_tag_clear(&mapping->page_tree,
> 1324 page_index(page),
> 1325 PAGECACHE_TAG_WRITEBACK);
> 1326 if (bdi_cap_account_writeback(bdi)) {
> 1327 __dec_bdi_stat(bdi, BDI_WRITEBACK);
> 1328 __bdi_writeout_inc(bdi);
> 1329 }
> 1330 }
> 1331 spin_unlock_irqrestore(&mapping->tree_lock, flags);
> 1332 } else {
> 1333 ret = TestClearPageWriteback(page);
> 1334 }
> 1335 if (ret)
> 1336 dec_zone_page_state(page, NR_WRITEBACK);
> 1337 return ret;
> 1338 }
We can move this up to under tree_lock. Considering memcg, all our target has "mapping".
If we newly account bounce-buffers (for NILFS, FUSE, etc..), which has no ->mapping,
we need much more complex new charge/uncharge theory.
But yes, adding new lock scheme seems complicated. (Sorry Andrea.)
My concerns is performance. We may need somehing new re-implementation of
locks/migrate/charge/uncharge.
Thanks,
-Kame
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