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SubjectRe: [PATCH] zsmalloc: zs_page_migrate: not check inuse if migrate_mode is not MIGRATE_ASYNC
Hello Hui,

On Fri, Jul 14, 2017 at 03:51:07PM +0800, Hui Zhu wrote:
> Got some -EBUSY from zs_page_migrate that will make migration
> slow (retry) or fail (zs_page_putback will schedule_work free_work,
> but it cannot ensure the success).

I think EAGAIN(migration retrial) is better than EBUSY(bailout) because
expectation is that zsmalloc will release the empty zs_page soon so
at next retrial, it will be succeeded.
About schedule_work, as you said, we don't make sure when it happens but
I believe it will happen in a migration iteration most of case.
How often do you see that case?

>
> And I didn't find anything that make zs_page_migrate cannot work with
> a ZS_EMPTY zspage.
> So make the patch to not check inuse if migrate_mode is not
> MIGRATE_ASYNC.

At a first glance, I think it work but the question is that it a same problem
ith schedule_work of zs_page_putback. IOW, Until the work is done, compaction
cannot succeed. Do you have any number before and after?

Thanks.

>
> Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
> ---
> mm/zsmalloc.c | 66 +++++++++++++++++++++++++++++++++--------------------------
> 1 file changed, 37 insertions(+), 29 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index d41edd2..c298e5c 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1982,6 +1982,7 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
> unsigned long old_obj, new_obj;
> unsigned int obj_idx;
> int ret = -EAGAIN;
> + int inuse;
>
> VM_BUG_ON_PAGE(!PageMovable(page), page);
> VM_BUG_ON_PAGE(!PageIsolated(page), page);
> @@ -1996,21 +1997,24 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
> offset = get_first_obj_offset(page);
>
> spin_lock(&class->lock);
> - if (!get_zspage_inuse(zspage)) {
> + inuse = get_zspage_inuse(zspage);
> + if (mode == MIGRATE_ASYNC && !inuse) {
> ret = -EBUSY;
> goto unlock_class;
> }
>
> pos = offset;
> s_addr = kmap_atomic(page);
> - while (pos < PAGE_SIZE) {
> - head = obj_to_head(page, s_addr + pos);
> - if (head & OBJ_ALLOCATED_TAG) {
> - handle = head & ~OBJ_ALLOCATED_TAG;
> - if (!trypin_tag(handle))
> - goto unpin_objects;
> + if (inuse) {
> + while (pos < PAGE_SIZE) {
> + head = obj_to_head(page, s_addr + pos);
> + if (head & OBJ_ALLOCATED_TAG) {
> + handle = head & ~OBJ_ALLOCATED_TAG;
> + if (!trypin_tag(handle))
> + goto unpin_objects;
> + }
> + pos += class->size;
> }
> - pos += class->size;
> }
>
> /*
> @@ -2020,20 +2024,22 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
> memcpy(d_addr, s_addr, PAGE_SIZE);
> kunmap_atomic(d_addr);
>
> - for (addr = s_addr + offset; addr < s_addr + pos;
> - addr += class->size) {
> - head = obj_to_head(page, addr);
> - if (head & OBJ_ALLOCATED_TAG) {
> - handle = head & ~OBJ_ALLOCATED_TAG;
> - if (!testpin_tag(handle))
> - BUG();
> -
> - old_obj = handle_to_obj(handle);
> - obj_to_location(old_obj, &dummy, &obj_idx);
> - new_obj = (unsigned long)location_to_obj(newpage,
> - obj_idx);
> - new_obj |= BIT(HANDLE_PIN_BIT);
> - record_obj(handle, new_obj);
> + if (inuse) {
> + for (addr = s_addr + offset; addr < s_addr + pos;
> + addr += class->size) {
> + head = obj_to_head(page, addr);
> + if (head & OBJ_ALLOCATED_TAG) {
> + handle = head & ~OBJ_ALLOCATED_TAG;
> + if (!testpin_tag(handle))
> + BUG();
> +
> + old_obj = handle_to_obj(handle);
> + obj_to_location(old_obj, &dummy, &obj_idx);
> + new_obj = (unsigned long)
> + location_to_obj(newpage, obj_idx);
> + new_obj |= BIT(HANDLE_PIN_BIT);
> + record_obj(handle, new_obj);
> + }
> }
> }
>
> @@ -2055,14 +2061,16 @@ int zs_page_migrate(struct address_space *mapping, struct page *newpage,
>
> ret = MIGRATEPAGE_SUCCESS;
> unpin_objects:
> - for (addr = s_addr + offset; addr < s_addr + pos;
> + if (inuse) {
> + for (addr = s_addr + offset; addr < s_addr + pos;
> addr += class->size) {
> - head = obj_to_head(page, addr);
> - if (head & OBJ_ALLOCATED_TAG) {
> - handle = head & ~OBJ_ALLOCATED_TAG;
> - if (!testpin_tag(handle))
> - BUG();
> - unpin_tag(handle);
> + head = obj_to_head(page, addr);
> + if (head & OBJ_ALLOCATED_TAG) {
> + handle = head & ~OBJ_ALLOCATED_TAG;
> + if (!testpin_tag(handle))
> + BUG();
> + unpin_tag(handle);
> + }
> }
> }
> kunmap_atomic(s_addr);
> --
> 1.9.1
>
> --
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