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Message-ID: <CAF8kJuPqTWdxdUnU_0b4JNY06S6qdc5rEDwtr6M6NV9PhmHVUw@mail.gmail.com>
Date: Tue, 18 Jun 2024 03:01:42 -0700
From: Chris Li <chrisl@...nel.org>
To: "Huang, Ying" <ying.huang@...el.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>, Kairui Song <kasong@...cent.com>,
Ryan Roberts <ryan.roberts@....com>, Kalesh Singh <kaleshsingh@...gle.com>,
linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Barry Song <baohua@...nel.org>
Subject: Re: [PATCH v2 1/2] mm: swap: swap cluster switch to double link list
On Tue, Jun 18, 2024 at 12:56 AM Huang, Ying <ying.huang@...el.com> wrote:
>
> Chris Li <chrisl@...nel.org> writes:
>
> > On Sun, Jun 16, 2024 at 11:21 PM Huang, Ying <ying.huang@...el.com> wrote:
> >>
> >> Hi, Chris,
> >>
> >> Chris Li <chrisl@...nel.org> writes:
> >>
> >> > Previously, the swap cluster used a cluster index as a pointer
> >> > to construct a custom single link list type "swap_cluster_list".
> >> > The next cluster pointer is shared with the cluster->count.
> >> > It prevents puting the non free cluster into a list.
> >> > Change the cluster to use the standard double link list instead.
> >> > This allows tracing the nonfull cluster in the follow up patch.
> >> >
> >> > Remove the cluster getter/setter for accessing the cluster
> >> > struct member.
> >> >
> >> > The list operation is protected by the swap_info_struct->lock.
> >> >
> >> > Change cluster code to use "struct swap_cluster_info *" to
> >> > reference the cluster rather than by using index. That is more
> >> > consistent with the list manipulation. It avoids the repeat
> >> > adding index to the cluser_info. The code is easier to understand.
> >> >
> >> > Remove the cluster next pointer is NULL flag, the double link
> >> > list can handle the empty list pretty well.
> >>
> >> The above is more about "what" instead of "why". We can identify "what"
> >> from the patch itself. I expect more "why". I guess that we can reduce
> >> swap_map[] scanning if we have lists of non-full/non-free clusters.
> >
> > In my mind, the "why" is captured by " This allows tracing the nonfull
> > cluster in the follow up patch.".
> > If you want to ask "why" we want the "nonfull cluster list". It is to
> > get to the suitable candidate cluster with that order quicker than
> > scanning swap_map[].
>
> Good. Please add that into the patch description. And I think that we
> can reduce the description about "what" too.
Sure.
>
> >>
> >> > The "swap_cluster_info" struct is two pointer bigger, because
> >> > 512 swap entries share one swap struct, it has very little impact
> >> > on the average memory usage per swap entry. For 1TB swapfile, the
> >> > swap cluster data structure increases from 8MB to 24MB.
> >> >
> >> > Other than the list conversion, there is no real function change
> >> > in this patch.
> >> >
> >> > Signed-off-by: Chris Li <chrisl@...nel.org>
> >> > ---
> >> > include/linux/swap.h | 28 +++----
> >> > mm/swapfile.c | 227 +++++++++++++--------------------------------------
> >> > 2 files changed, 70 insertions(+), 185 deletions(-)
> >> >
> >> > diff --git a/include/linux/swap.h b/include/linux/swap.h
> >> > index 3df75d62a835..cd9154a3e934 100644
> >> > --- a/include/linux/swap.h
> >> > +++ b/include/linux/swap.h
> >> > @@ -242,23 +242,22 @@ enum {
> >> > * space with SWAPFILE_CLUSTER pages long and naturally aligns in disk. All
> >> > * free clusters are organized into a list. We fetch an entry from the list to
> >> > * get a free cluster.
> >> > - *
> >> > - * The data field stores next cluster if the cluster is free or cluster usage
> >> > - * counter otherwise. The flags field determines if a cluster is free. This is
> >> > - * protected by swap_info_struct.lock.
> >> > */
> >> > struct swap_cluster_info {
> >> > spinlock_t lock; /*
> >> > - * Protect swap_cluster_info fields
> >> > - * and swap_info_struct->swap_map
> >> > + * Protect swap_cluster_info count and state
> >>
> >> Protect swap_cluster_info fields except 'list' ?
> >
> > I change it to protect the swap_cluster_info bitfields in the second patch.
>
> Although I still prefer my version, I will not insist on that.
Sure, I actually don't have a strong preference about that. It is just comments.
>
> >>
> >> > + * field and swap_info_struct->swap_map
> >> > * elements correspond to the swap
> >> > * cluster
> >> > */
> >> > - unsigned int data:24;
> >> > - unsigned int flags:8;
> >> > + unsigned int count:12;
> >> > + unsigned int state:3;
> >>
> >> I still prefer normal data type over bit fields. How about
> >>
> >> u16 usage;
> >> u8 state;
> >
> > I don't mind the "count" rename to "usage". That is probably a better
> > name. However I have another patch intended to add more bit fields in
> > the cluster info struct. The second patch adds "order" and the later
> > patch will add more. That is why I choose bitfield to be more condense
> > with bits.
>
> We still have space for another "u8" for "order". It appears trivial to
> change it to bit fields when necessary in the future.
We can, I don't see it necessary to change from bit field to u8 and
back to bit field in the future. It is more of a personal preference
issue.
> >>
> >> And, how about use 'usage' instead of 'count'? Personally I think that
> >> it is more clear. But I don't have strong opinions on this.
> >>
> >> > + struct list_head list; /* Protected by swap_info_struct->lock */
> >> > };
> >> > -#define CLUSTER_FLAG_FREE 1 /* This cluster is free */
> >> > -#define CLUSTER_FLAG_NEXT_NULL 2 /* This cluster has no next cluster */
> >> > +
> >> > +#define CLUSTER_STATE_FREE 1 /* This cluster is free */
> >>
> >> Can we use swap_cluster_info->count == 0?
> >
> > It is not as good considering the second patch starts to track the
> > state of the cluster of per cpu struct. We will be comparing both the
> > cluster->count and cluster->state.
> >
> >>
> >> > +#define CLUSTER_STATE_PER_CPU 2 /* This cluster on per_cpu_cluster */
> >> > +
> >>
> >> There's no users of this state in this patch. IMHO, it's better to
> >
> > Yes, there is usage of this state in this patch in the sense that, if
> > you remove that state definition,
> > the code can't compile due to assignment of CLUSTER_STATE_PER_CPU.
>
> Sorry, my words were confusing, we can move both the assignment and the
> state itself to the second patch.
>
> > There is a code test if a cluster state is not a free state, which
> > excludes "CLUSTER_STATE_PER_CPU".
>
> You mean the functionality that is equivalent to original
> cluster_set_count_flag(0, 0) and cluster_is_free()? I think
> CLUSTER_STATE_PER_CPU cannot catch all. If so, I suggest you to keep
> swap_cluster_info.flags and CLUSTER_FLAG_FREE in this patch and change
> it in the 2nd patch. That will make this patch more focused and easier
> to be reviewed.
That is one way to do it.
>
> In general, please try to keep this patch as simple as possible to help
> reviewers. Because it's quite long. For example, just convert the list
> implementation and keep other stuff as much as possible.
>
Let me think about it. Thanks.
> >> introduce a symbol with its users, otherwise, it's hard to understand
> >> why do we need it and how to use it. And, IIUC, the state isn't
> >> maintained properly, it should be changed when we move the cluster off
> >> the per-cpu cluster.
> >
> > I am actually following the same usage principle as you suggested
> > here. Only the second patch starts to use the off per cpu state
> > (SCANNED). That is why I introduce it there.
> >
> >>
> >> > /*
> >> > * The first page in the swap file is the swap header, which is always marked
> >> > @@ -283,11 +282,6 @@ struct percpu_cluster {
> >> > unsigned int next[SWAP_NR_ORDERS]; /* Likely next allocation offset */
> >> > };
> >> >
> >> > -struct swap_cluster_list {
> >> > - struct swap_cluster_info head;
> >> > - struct swap_cluster_info tail;
> >> > -};
> >> > -
> >> > /*
> >> > * The in-memory structure used to track swap areas.
> >> > */
> >> > @@ -300,7 +294,7 @@ struct swap_info_struct {
> >> > unsigned int max; /* extent of the swap_map */
> >> > unsigned char *swap_map; /* vmalloc'ed array of usage counts */
> >> > struct swap_cluster_info *cluster_info; /* cluster info. Only for SSD */
> >> > - struct swap_cluster_list free_clusters; /* free clusters list */
> >> > + struct list_head free_clusters; /* free clusters list */
> >> > unsigned int lowest_bit; /* index of first free in swap_map */
> >> > unsigned int highest_bit; /* index of last free in swap_map */
> >> > unsigned int pages; /* total of usable pages of swap */
> >> > @@ -331,7 +325,7 @@ struct swap_info_struct {
> >> > * list.
> >> > */
> >> > struct work_struct discard_work; /* discard worker */
> >> > - struct swap_cluster_list discard_clusters; /* discard clusters list */
> >> > + struct list_head discard_clusters; /* discard clusters list */
> >> > struct plist_node avail_lists[]; /*
> >> > * entries in swap_avail_heads, one
> >> > * entry per node.
> >> > diff --git a/mm/swapfile.c b/mm/swapfile.c
> >> > index 9c6d8e557c0f..2f878b374349 100644
> >> > --- a/mm/swapfile.c
> >> > +++ b/mm/swapfile.c
> >> > @@ -290,62 +290,9 @@ static void discard_swap_cluster(struct swap_info_struct *si,
> >> > #endif
> >> > #define LATENCY_LIMIT 256
> >> >
> >> > -static inline void cluster_set_flag(struct swap_cluster_info *info,
> >> > - unsigned int flag)
> >> > -{
> >> > - info->flags = flag;
> >> > -}
> >> > -
> >> > -static inline unsigned int cluster_count(struct swap_cluster_info *info)
> >> > -{
> >> > - return info->data;
> >> > -}
> >> > -
> >> > -static inline void cluster_set_count(struct swap_cluster_info *info,
> >> > - unsigned int c)
> >> > -{
> >> > - info->data = c;
> >> > -}
> >> > -
> >> > -static inline void cluster_set_count_flag(struct swap_cluster_info *info,
> >> > - unsigned int c, unsigned int f)
> >> > -{
> >> > - info->flags = f;
> >> > - info->data = c;
> >> > -}
> >> > -
> >> > -static inline unsigned int cluster_next(struct swap_cluster_info *info)
> >> > -{
> >> > - return info->data;
> >> > -}
> >> > -
> >> > -static inline void cluster_set_next(struct swap_cluster_info *info,
> >> > - unsigned int n)
> >> > -{
> >> > - info->data = n;
> >> > -}
> >> > -
> >> > -static inline void cluster_set_next_flag(struct swap_cluster_info *info,
> >> > - unsigned int n, unsigned int f)
> >> > -{
> >> > - info->flags = f;
> >> > - info->data = n;
> >> > -}
> >> > -
> >> > static inline bool cluster_is_free(struct swap_cluster_info *info)
> >> > {
> >> > - return info->flags & CLUSTER_FLAG_FREE;
> >> > -}
> >> > -
> >> > -static inline bool cluster_is_null(struct swap_cluster_info *info)
> >> > -{
> >> > - return info->flags & CLUSTER_FLAG_NEXT_NULL;
> >> > -}
> >> > -
> >> > -static inline void cluster_set_null(struct swap_cluster_info *info)
> >> > -{
> >> > - info->flags = CLUSTER_FLAG_NEXT_NULL;
> >> > - info->data = 0;
> >> > + return info->state == CLUSTER_STATE_FREE;
> >> > }
> >> >
> >> > static inline struct swap_cluster_info *lock_cluster(struct swap_info_struct *si,
> >> > @@ -394,65 +341,11 @@ static inline void unlock_cluster_or_swap_info(struct swap_info_struct *si,
> >> > spin_unlock(&si->lock);
> >> > }
> >> >
> >> > -static inline bool cluster_list_empty(struct swap_cluster_list *list)
> >> > -{
> >> > - return cluster_is_null(&list->head);
> >> > -}
> >> > -
> >> > -static inline unsigned int cluster_list_first(struct swap_cluster_list *list)
> >> > -{
> >> > - return cluster_next(&list->head);
> >> > -}
> >> > -
> >> > -static void cluster_list_init(struct swap_cluster_list *list)
> >> > -{
> >> > - cluster_set_null(&list->head);
> >> > - cluster_set_null(&list->tail);
> >> > -}
> >> > -
> >> > -static void cluster_list_add_tail(struct swap_cluster_list *list,
> >> > - struct swap_cluster_info *ci,
> >> > - unsigned int idx)
> >> > -{
> >> > - if (cluster_list_empty(list)) {
> >> > - cluster_set_next_flag(&list->head, idx, 0);
> >> > - cluster_set_next_flag(&list->tail, idx, 0);
> >> > - } else {
> >> > - struct swap_cluster_info *ci_tail;
> >> > - unsigned int tail = cluster_next(&list->tail);
> >> > -
> >> > - /*
> >> > - * Nested cluster lock, but both cluster locks are
> >> > - * only acquired when we held swap_info_struct->lock
> >> > - */
> >> > - ci_tail = ci + tail;
> >> > - spin_lock_nested(&ci_tail->lock, SINGLE_DEPTH_NESTING);
> >> > - cluster_set_next(ci_tail, idx);
> >> > - spin_unlock(&ci_tail->lock);
> >> > - cluster_set_next_flag(&list->tail, idx, 0);
> >> > - }
> >> > -}
> >> > -
> >> > -static unsigned int cluster_list_del_first(struct swap_cluster_list *list,
> >> > - struct swap_cluster_info *ci)
> >> > -{
> >> > - unsigned int idx;
> >> > -
> >> > - idx = cluster_next(&list->head);
> >> > - if (cluster_next(&list->tail) == idx) {
> >> > - cluster_set_null(&list->head);
> >> > - cluster_set_null(&list->tail);
> >> > - } else
> >> > - cluster_set_next_flag(&list->head,
> >> > - cluster_next(&ci[idx]), 0);
> >> > -
> >> > - return idx;
> >> > -}
> >> > -
> >> > /* Add a cluster to discard list and schedule it to do discard */
> >> > static void swap_cluster_schedule_discard(struct swap_info_struct *si,
> >> > - unsigned int idx)
> >> > + struct swap_cluster_info *ci)
> >> > {
> >> > + unsigned int idx = ci - si->cluster_info;
> >>
> >> I see this multiple times in the patch, can we define a helper for this?
> > Ack.
> >
> >>
> >> > /*
> >> > * If scan_swap_map_slots() can't find a free cluster, it will check
> >> > * si->swap_map directly. To make sure the discarding cluster isn't
> >> > @@ -462,17 +355,14 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
> >> > memset(si->swap_map + idx * SWAPFILE_CLUSTER,
> >> > SWAP_MAP_BAD, SWAPFILE_CLUSTER);
> >> >
> >> > - cluster_list_add_tail(&si->discard_clusters, si->cluster_info, idx);
> >> > -
> >> > + list_add_tail(&ci->list, &si->discard_clusters);
> >> > schedule_work(&si->discard_work);
> >> > }
> >> >
> >> > -static void __free_cluster(struct swap_info_struct *si, unsigned long idx)
> >> > +static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
> >> > {
> >> > - 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);
> >> > + ci->state = CLUSTER_STATE_FREE;
> >> > + list_add_tail(&ci->list, &si->free_clusters);
> >> > }
> >> >
> >> > /*
> >> > @@ -481,21 +371,22 @@ static void __free_cluster(struct swap_info_struct *si, unsigned long idx)
> >> > */
> >> > static void swap_do_scheduled_discard(struct swap_info_struct *si)
> >> > {
> >> > - struct swap_cluster_info *info, *ci;
> >> > + struct swap_cluster_info *ci;
> >> > unsigned int idx;
> >> >
> >> > - info = si->cluster_info;
> >> > -
> >> > - while (!cluster_list_empty(&si->discard_clusters)) {
> >> > - idx = cluster_list_del_first(&si->discard_clusters, info);
> >> > + while (!list_empty(&si->discard_clusters)) {
> >> > + ci = list_first_entry(&si->discard_clusters, struct swap_cluster_info, list);
> >> > + list_del(&ci->list);
> >> > + idx = ci - si->cluster_info;
> >> > spin_unlock(&si->lock);
> >> >
> >> > discard_swap_cluster(si, idx * SWAPFILE_CLUSTER,
> >> > SWAPFILE_CLUSTER);
> >> >
> >> > spin_lock(&si->lock);
> >> > - ci = lock_cluster(si, idx * SWAPFILE_CLUSTER);
> >> > - __free_cluster(si, idx);
> >> > +
> >> > + spin_lock(&ci->lock);
> >>
> >> Personally, I still prefer to use lock_cluster(), which is more readable
> >> and matches unlock_cluster() below.
> >
> > lock_cluster() uses an index which is not matching unlock_cluster()
> > which is using a pointer to cluster.
>
> lock_cluster()/unlock_cluster() are pair and fit original design
> well. They use different parameter because swap cluster is optional.
>
> > When you get the cluster from the list, you have a cluster pointer. I
> > feel it is unnecessary to convert to index then back convert to
> > cluster pointer inside lock_cluster(). I actually feel using indexes
> > to refer to the cluster is error prone because we also have offset.
>
> I don't think so, it's common to use swap offset.
Swap offset is not an issue, it is all over the place. The cluster
index(offset/512) is the one I try to avoid.
I have made some mistakes myself on offset vs index.
>
> >
> >>
> >> > + __free_cluster(si, ci);
> >> > memset(si->swap_map + idx * SWAPFILE_CLUSTER,
> >> > 0, SWAPFILE_CLUSTER);
> >> > unlock_cluster(ci);
> >> > @@ -521,20 +412,19 @@ static void swap_users_ref_free(struct percpu_ref *ref)
> >> > complete(&si->comp);
> >> > }
> >> >
> >> > -static void alloc_cluster(struct swap_info_struct *si, unsigned long idx)
> >> > +static struct swap_cluster_info *alloc_cluster(struct swap_info_struct *si, unsigned long idx)
> >> > {
> >> > - struct swap_cluster_info *ci = si->cluster_info;
> >> > + struct swap_cluster_info *ci = list_first_entry(&si->free_clusters, struct swap_cluster_info, list);
> >> >
> >> > - VM_BUG_ON(cluster_list_first(&si->free_clusters) != idx);
> >> > - cluster_list_del_first(&si->free_clusters, ci);
> >> > - cluster_set_count_flag(ci + idx, 0, 0);
> >> > + VM_BUG_ON(ci - si->cluster_info != idx);
> >> > + list_del(&ci->list);
> >> > + ci->count = 0;
> >>
> >> Do we need this now? If we keep CLUSTER_STATE_FREE, we need to change
> >> it here.
> >
> > Good catch, thanks for catching that. Now I realized this is actually
> > problematic and tricky to get it right. Let me work on that.
> >
> >>
> >> > + return ci;
> >> > }
> >> >
> >> > -static void free_cluster(struct swap_info_struct *si, unsigned long idx)
> >> > +static void free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
> >> > {
> >> > - struct swap_cluster_info *ci = si->cluster_info + idx;
> >> > -
> >> > - VM_BUG_ON(cluster_count(ci) != 0);
> >> > + VM_BUG_ON(ci->count != 0);
> >> > /*
> >> > * If the swap is discardable, prepare discard the cluster
> >> > * instead of free it immediately. The cluster will be freed
> >> > @@ -542,11 +432,11 @@ static void free_cluster(struct swap_info_struct *si, unsigned long idx)
> >> > */
> >> > if ((si->flags & (SWP_WRITEOK | SWP_PAGE_DISCARD)) ==
> >> > (SWP_WRITEOK | SWP_PAGE_DISCARD)) {
> >> > - swap_cluster_schedule_discard(si, idx);
> >> > + swap_cluster_schedule_discard(si, ci);
> >> > return;
> >> > }
> >> >
> >> > - __free_cluster(si, idx);
> >> > + __free_cluster(si, ci);
> >> > }
> >> >
> >> > /*
> >> > @@ -559,15 +449,15 @@ static void add_cluster_info_page(struct swap_info_struct *p,
> >> > unsigned long count)
> >> > {
> >> > unsigned long idx = page_nr / SWAPFILE_CLUSTER;
> >> > + struct swap_cluster_info *ci = cluster_info + idx;
> >> >
> >> > if (!cluster_info)
> >> > return;
> >> > - if (cluster_is_free(&cluster_info[idx]))
> >> > + if (cluster_is_free(ci))
> >> > alloc_cluster(p, idx);
> >> >
> >> > - VM_BUG_ON(cluster_count(&cluster_info[idx]) + count > SWAPFILE_CLUSTER);
> >> > - cluster_set_count(&cluster_info[idx],
> >> > - cluster_count(&cluster_info[idx]) + count);
> >> > + VM_BUG_ON(ci->count + count > SWAPFILE_CLUSTER);
> >> > + ci->count += count;
> >> > }
> >> >
> >> > /*
> >> > @@ -581,24 +471,20 @@ static void inc_cluster_info_page(struct swap_info_struct *p,
> >> > }
> >> >
> >> > /*
> >> > - * The cluster corresponding to page_nr decreases one usage. If the usage
> >> > - * counter becomes 0, which means no page in the cluster is in using, we can
> >> > - * optionally discard the cluster and add it to free cluster list.
> >> > + * The cluster ci decreases one usage. If the usage counter becomes 0,
> >> > + * which means no page in the cluster is in using, we can optionally discard
> >> > + * the cluster and add it to free cluster list.
> >> > */
> >> > -static void dec_cluster_info_page(struct swap_info_struct *p,
> >> > - struct swap_cluster_info *cluster_info, unsigned long page_nr)
> >> > +static void dec_cluster_info_page(struct swap_info_struct *p, struct swap_cluster_info *ci)
> >> > {
> >> > - unsigned long idx = page_nr / SWAPFILE_CLUSTER;
> >> > -
> >> > - if (!cluster_info)
> >> > + if (!p->cluster_info)
> >> > return;
> >> >
> >> > - VM_BUG_ON(cluster_count(&cluster_info[idx]) == 0);
> >> > - cluster_set_count(&cluster_info[idx],
> >> > - cluster_count(&cluster_info[idx]) - 1);
> >> > + VM_BUG_ON(ci->count == 0);
> >> > + ci->count--;
> >> >
> >> > - if (cluster_count(&cluster_info[idx]) == 0)
> >> > - free_cluster(p, idx);
> >> > + if (!ci->count)
> >> > + free_cluster(p, ci);
> >> > }
> >> >
> >> > /*
> >> > @@ -611,10 +497,10 @@ scan_swap_map_ssd_cluster_conflict(struct swap_info_struct *si,
> >> > {
> >> > struct percpu_cluster *percpu_cluster;
> >> > bool conflict;
> >> > -
> >>
> >> Usually we use one blank line after local variable declaration.
> > Ack.
> >
> >>
> >> > + struct swap_cluster_info *first = list_first_entry(&si->free_clusters, struct swap_cluster_info, list);
> >> > offset /= SWAPFILE_CLUSTER;
> >> > - conflict = !cluster_list_empty(&si->free_clusters) &&
> >> > - offset != cluster_list_first(&si->free_clusters) &&
> >> > + conflict = !list_empty(&si->free_clusters) &&
> >> > + offset != first - si->cluster_info &&
> >> > cluster_is_free(&si->cluster_info[offset]);
> >> >
> >> > if (!conflict)
> >> > @@ -655,10 +541,14 @@ static bool scan_swap_map_try_ssd_cluster(struct swap_info_struct *si,
> >> > cluster = this_cpu_ptr(si->percpu_cluster);
> >> > tmp = cluster->next[order];
> >> > if (tmp == SWAP_NEXT_INVALID) {
> >> > - if (!cluster_list_empty(&si->free_clusters)) {
> >> > - tmp = cluster_next(&si->free_clusters.head) *
> >> > - SWAPFILE_CLUSTER;
> >> > - } else if (!cluster_list_empty(&si->discard_clusters)) {
> >> > + if (!list_empty(&si->free_clusters)) {
> >> > + ci = list_first_entry(&si->free_clusters, struct swap_cluster_info, list);
> >> > + list_del(&ci->list);
> >>
> >> The free cluster is deleted from si->free_clusters now. But later you
> >> will call scan_swap_map_ssd_cluster_conflict() and may abandon the
> >> cluster. And in alloc_cluster() later, it may be deleted again.
> >
> > Yes, that is a bug. Thanks for catching that.
> >
> >>
> >> > + spin_lock(&ci->lock);
> >> > + ci->state = CLUSTER_STATE_PER_CPU;
> >>
> >> Need to change ci->state when move a cluster off the percpu_cluster.
> >
> > In the next patch. This patch does not use the off state yet.
>
> But that is confusing to use wrong state name, the really meaning is
> something like CLUSTER_STATE_NON_FREE. But as I suggested above, we can
It can be FREE and on the per cpu pointer as well. That is the tricky part.
It can happen on the current code as well.
> keep swap_cluster_info.flags and CLUSTER_FLAG_FREE in this patch.
Maybe. Will consider that.
>
> >>
> >> > + spin_unlock(&ci->lock);
> >> > + tmp = (ci - si->cluster_info) * SWAPFILE_CLUSTER;
> >> > + } else if (!list_empty(&si->discard_clusters)) {
> >> > /*
> >> > * we don't have free cluster but have some clusters in
> >> > * discarding, do discard now and reclaim them, then
> >> > @@ -1062,8 +952,8 @@ static void swap_free_cluster(struct swap_info_struct *si, unsigned long idx)
> >> >
> >> > ci = lock_cluster(si, offset);
> >> > memset(si->swap_map + offset, 0, SWAPFILE_CLUSTER);
> >> > - cluster_set_count_flag(ci, 0, 0);
> >> > - free_cluster(si, idx);
> >> > + ci->count = 0;
> >> > + free_cluster(si, ci);
> >> > unlock_cluster(ci);
> >> > swap_range_free(si, offset, SWAPFILE_CLUSTER);
> >> > }
> >> > @@ -1336,7 +1226,7 @@ static void swap_entry_free(struct swap_info_struct *p, swp_entry_t entry)
> >> > count = p->swap_map[offset];
> >> > VM_BUG_ON(count != SWAP_HAS_CACHE);
> >> > p->swap_map[offset] = 0;
> >> > - dec_cluster_info_page(p, p->cluster_info, offset);
> >> > + dec_cluster_info_page(p, ci);
> >> > unlock_cluster(ci);
> >> >
> >> > mem_cgroup_uncharge_swap(entry, 1);
> >> > @@ -3003,8 +2893,8 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
> >> >
> >> > nr_good_pages = maxpages - 1; /* omit header page */
> >> >
> >> > - cluster_list_init(&p->free_clusters);
> >> > - cluster_list_init(&p->discard_clusters);
> >> > + INIT_LIST_HEAD(&p->free_clusters);
> >> > + INIT_LIST_HEAD(&p->discard_clusters);
> >> >
> >> > for (i = 0; i < swap_header->info.nr_badpages; i++) {
> >> > unsigned int page_nr = swap_header->info.badpages[i];
> >> > @@ -3055,14 +2945,15 @@ static int setup_swap_map_and_extents(struct swap_info_struct *p,
> >> > for (k = 0; k < SWAP_CLUSTER_COLS; k++) {
> >> > j = (k + col) % SWAP_CLUSTER_COLS;
> >> > for (i = 0; i < DIV_ROUND_UP(nr_clusters, SWAP_CLUSTER_COLS); i++) {
> >> > + struct swap_cluster_info *ci;
> >> > idx = i * SWAP_CLUSTER_COLS + j;
> >> > + ci = cluster_info + idx;
> >> > if (idx >= nr_clusters)
> >> > continue;
> >> > - if (cluster_count(&cluster_info[idx]))
> >> > + if (ci->count)
> >> > continue;
> >> > - cluster_set_flag(&cluster_info[idx], CLUSTER_FLAG_FREE);
> >> > - cluster_list_add_tail(&p->free_clusters, cluster_info,
> >> > - idx);
> >> > + ci->state = CLUSTER_STATE_FREE;
> >> > + list_add_tail(&ci->list, &p->free_clusters);
> >> > }
> >> > }
> >> > return nr_extents;
> >
> > Thank you for the review and spotting the bug.
>
> My pleasure!
Thanks!
Chris
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