Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> writes:
> On Wed, 2017-03-15 at 09:19 +0800, Huang, Ying wrote:
>> Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx> writes:
>>
>> >
>> > On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote:
>> > >
>> > > From: Huang Ying <ying.huang@xxxxxxxxx>
>> > >
>> > > 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 <aarcange@xxxxxxxxxx>
>> > > Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
>> > > Cc: Hugh Dickins <hughd@xxxxxxxxxx>
>> > > Cc: Shaohua Li <shli@xxxxxxxxxx>
>> > > Cc: Minchan Kim <minchan@xxxxxxxxxx>
>> > > Cc: Rik van Riel <riel@xxxxxxxxxx>
>> > > Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
>> > > ---
>> > > 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
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