>>>>> "Sasha" == Sasha Levin <sashal@xxxxxxxxxx> writes: Sasha> From: Coly Li <colyli@xxxxxxx> Sasha> [ Upstream commit 9fcc34b1a6dd4b8e5337e2b6ef45e428897eca6b ] Sasha> In bch_mca_scan(), the number of shrinking btree node is calculated Sasha> by code like this, Sasha> unsigned long nr = sc->nr_to_scan; Sasha> nr /= c->btree_pages; Sasha> nr = min_t(unsigned long, nr, mca_can_free(c)); Sasha> variable sc->nr_to_scan is number of objects (here is bcache B+tree Sasha> nodes' number) to shrink, and pointer variable sc is sent from memory Sasha> management code as parametr of a callback. Sasha> If sc->nr_to_scan is smaller than c->btree_pages, after the above Sasha> calculation, variable 'nr' will be 0 and nothing will be shrunk. It is Sasha> frequeently observed that only 1 or 2 is set to sc->nr_to_scan and make Sasha> nr to be zero. Then bch_mca_scan() will do nothing more then acquiring Sasha> and releasing mutex c->bucket_lock. Sasha> This patch checkes whether nr is 0 after the above calculation, if 0 Sasha> is the result then set 1 to variable 'n'. Then at least bch_mca_scan() Sasha> will try to shrink a single B+tree node. Sasha> nr /= c->btree_pages; Sasha> + if (nr == 0) Sasha> + nr = 1; Wouldn't it be even more clear with: nr /= c->bree_pages || 1; instead? John
