Tim Chen <[email protected]> writes: > On Wed, 2017-03-15 at 09:19 +0800, Huang, Ying wrote: >> Tim Chen <[email protected]> writes: >> >> > >> > On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote: >> > > >> > > From: Huang Ying <[email protected]> >> > > >> > > The swap cluster allocation/free functions are added based on the >> > > existing swap cluster management mechanism for SSD. These functions >> > > don't work for the rotating hard disks because the existing swap cluster >> > > management mechanism doesn't work for them. The hard disks support may >> > > be added if someone really need it. But that needn't be included in >> > > this patchset. >> > > >> > > This will be used for the THP (Transparent Huge Page) swap support. >> > > Where one swap cluster will hold the contents of each THP swapped out. >> > > >> > > Cc: Andrea Arcangeli <[email protected]> >> > > Cc: Kirill A. Shutemov <[email protected]> >> > > Cc: Hugh Dickins <[email protected]> >> > > Cc: Shaohua Li <[email protected]> >> > > Cc: Minchan Kim <[email protected]> >> > > Cc: Rik van Riel <[email protected]> >> > > Signed-off-by: "Huang, Ying" <[email protected]> >> > > --- >> > > mm/swapfile.c | 217 >> > > +++++++++++++++++++++++++++++++++++++++++----------------- >> > > 1 file changed, 156 insertions(+), 61 deletions(-) >> > > >> > > diff --git a/mm/swapfile.c b/mm/swapfile.c >> > > index a744604384ff..91876c33114b 100644 >> > > --- a/mm/swapfile.c >> > > +++ b/mm/swapfile.c >> > > @@ -378,6 +378,14 @@ static void swap_cluster_schedule_discard(struct >> > > swap_info_struct *si, >> > > schedule_work(&si->discard_work); >> > > } >> > > >> > > +static void __free_cluster(struct swap_info_struct *si, unsigned long >> > > idx) >> > > +{ >> > > + struct swap_cluster_info *ci = si->cluster_info; >> > > + >> > > + cluster_set_flag(ci + idx, CLUSTER_FLAG_FREE); >> > > + cluster_list_add_tail(&si->free_clusters, ci, idx); >> > > +} >> > > + >> > > /* >> > > * Doing discard actually. After a cluster discard is finished, the >> > > cluster >> > > * will be added to free cluster list. caller should hold si->lock. >> > > @@ -398,10 +406,7 @@ static void swap_do_scheduled_discard(struct >> > > swap_info_struct *si) >> > > >> > > spin_lock(&si->lock); >> > > ci = lock_cluster(si, idx * SWAPFILE_CLUSTER); >> > > - cluster_set_flag(ci, CLUSTER_FLAG_FREE); >> > > - unlock_cluster(ci); >> > > - cluster_list_add_tail(&si->free_clusters, info, idx); >> > > - ci = lock_cluster(si, idx * SWAPFILE_CLUSTER); >> > > + __free_cluster(si, idx); >> > > memset(si->swap_map + idx * SWAPFILE_CLUSTER, >> > > 0, SWAPFILE_CLUSTER); >> > > unlock_cluster(ci); >> > The __free_cluster definition and the above change to eliminate >> > the extra unlock_cluster and lock_cluster can perhaps be broken up >> > as a separate patch. It can be independent of THP changes. >> I think the change may have no value by itself without THP changes. >> There will be only 1 user of __free_cluster() and the lock change is >> trivial too. So I think it may be better just to keep it as that? >> > > Seems like the extra unlock and lock of cluster in existing code should be > taken out > irrespective of the THP changes: > > cluster_set_flag(ci, CLUSTER_FLAG_FREE); > - unlock_cluster(ci); > cluster_list_add_tail(&si->free_clusters, info, idx); > - ci = lock_cluster(si, idx * SWAPFILE_CLUSTER); > memset(si->swap_map + idx * SWAPFILE_CLUSTER, > 0, SWAPFILE_CLUSTER); >
This is not a functionality fix or performance optimization. Because the lock on the swap_info_struct is held during the operation and there are no operations on cluster with index "idx" in cluster_list_add_tail(). The change here is just to make the resulting code a little simpler. Is this deserved a separate patch? Best Regards, Huang, Ying
