Chris Li <chrisl@xxxxxxxxxx> writes: > Hi Ying, > > On Wed, May 29, 2024 at 1:57 AM Huang, Ying <ying.huang@xxxxxxxxx> wrote: >> >> Chris Li <chrisl@xxxxxxxxxx> writes: >> >> > I am spinning a new version for this series to address two issues >> > found in this series: >> > >> > 1) Oppo discovered a bug in the following line: >> > + ci = si->cluster_info + tmp; >> > Should be "tmp / SWAPFILE_CLUSTER" instead of "tmp". >> > That is a serious bug but trivial to fix. >> > >> > 2) order 0 allocation currently blindly scans swap_map disregarding >> > the cluster->order. >> >> IIUC, now, we only scan swap_map[] only if >> !list_empty(&si->free_clusters) && !list_empty(&si->nonfull_clusters[order]). >> That is, if you doesn't run low swap free space, you will not do that. > > You can still swap space in order 0 clusters while order 4 runs out of > free_cluster > or nonfull_clusters[order]. For Android that is a common case. When we fail to allocate order 4, we will fallback to order 0. Still don't need to scan swap_map[]. But after looking at your below reply, I realized that the swap space is almost full at most times in your cases. Then, it's possible that we run into scanning swap_map[]. list_empty(&si->free_clusters) && list_empty(&si->nonfull_clusters[order]) will become true, if we put too many clusters in si->percpu_cluster. So, if we want to avoid to scan swap_map[], we can stop add clusters in si->percpu_cluster when swap space runs low. And maybe take clusters out of si->percpu_cluster sometimes. Another issue is nonfull_cluster[order1] cannot be used for nonfull_cluster[order2]. In definition, we should not fail order 0 allocation, we need to steal nonfull_cluster[order>0] for order 0 allocation. This can avoid to scan swap_map[] too. This may be not perfect, but it is the simplest first step implementation. You can optimize based on it further. And, I checked your code again. It appears that si->percpu_cluster may be put in si->nonfull_cluster[], then be used by another CPU. Please check it. -- Best Regards, Huang, Ying [snip]
