[PATCH] zram: use copy_page for full page copy

[PATCH] zram: use copy_page for full page copy

[Jisheng Zhang]

commit 42e99bd975fd ("zram: optimize memory operations with
clear_page()/copy_page()") optimize page copy/clean operations, but
then commit d72e9a7a93e4 ("zram: do not use copy_page with non-page
aligned address") removes the optimization because there's memory
corruption at that time, the reason was well explained. But after
commit 1f7319c74275 ("zram: partial IO refactoring"), partial IO uses
alloc_page() instead of kmalloc to allocate a page, so we can bring
back the optimization.

commit 80ba4caf8ba9 ("zram: use copy_page for full page copy") brings
back partial optimization, missed one point in zram_write_page().
optimize the full page copying in zram_write_page() with copy_page()

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
---
 drivers/block/zram/zram_drv.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 3acd7006ad2c..4b2b5098062f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1478,11 +1478,13 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
 	dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
 
 	src = zstrm->buffer;
-	if (comp_len == PAGE_SIZE)
+	if (comp_len == PAGE_SIZE) {
 		src = kmap_local_page(page);
-	memcpy(dst, src, comp_len);
-	if (comp_len == PAGE_SIZE)
+		copy_page(dst, src);
 		kunmap_local(src);
+	} else {
+		memcpy(dst, src, comp_len);
+	}
 
 	zcomp_stream_put(zram->comps[ZRAM_PRIMARY_COMP]);
 	zs_unmap_object(zram->mem_pool, handle);
-- 
2.43.0

Re: [PATCH] zram: use copy_page for full page copy

[Sergey Senozhatsky]

On (24/06/13 08:04), Jisheng Zhang wrote:
> commit 42e99bd975fd ("zram: optimize memory operations with
> clear_page()/copy_page()") optimize page copy/clean operations, but
> then commit d72e9a7a93e4 ("zram: do not use copy_page with non-page
> aligned address") removes the optimization because there's memory
> corruption at that time, the reason was well explained. But after
> commit 1f7319c74275 ("zram: partial IO refactoring"), partial IO uses
> alloc_page() instead of kmalloc to allocate a page, so we can bring
> back the optimization.
> 
> commit 80ba4caf8ba9 ("zram: use copy_page for full page copy") brings
> back partial optimization, missed one point in zram_write_page().
> optimize the full page copying in zram_write_page() with copy_page()

Is copy_page() really more optimal than memcpy(PAGE_SIZE)?

Re: [PATCH] zram: use copy_page for full page copy

[Jisheng Zhang]

On Thu, Jun 13, 2024 at 12:17:31PM +0900, Sergey Senozhatsky wrote:
> On (24/06/13 08:04), Jisheng Zhang wrote:
> > commit 42e99bd975fd ("zram: optimize memory operations with
> > clear_page()/copy_page()") optimize page copy/clean operations, but
> > then commit d72e9a7a93e4 ("zram: do not use copy_page with non-page
> > aligned address") removes the optimization because there's memory
> > corruption at that time, the reason was well explained. But after
> > commit 1f7319c74275 ("zram: partial IO refactoring"), partial IO uses
> > alloc_page() instead of kmalloc to allocate a page, so we can bring
> > back the optimization.
> > 
> > commit 80ba4caf8ba9 ("zram: use copy_page for full page copy") brings
> > back partial optimization, missed one point in zram_write_page().
> > optimize the full page copying in zram_write_page() with copy_page()
> 
> Is copy_page() really more optimal than memcpy(PAGE_SIZE)?

I think yes copy_page performs better than memcpy(PAGE_SIZE)
commit afb2d666d025 ("zsmalloc: use copy_page for full page copy")
also shows the result.

Re: [PATCH] zram: use copy_page for full page copy

[Christoph Hellwig]

On Thu, Jun 13, 2024 at 08:04:22AM +0800, Jisheng Zhang wrote:
> commit 42e99bd975fd ("zram: optimize memory operations with
> clear_page()/copy_page()") optimize page copy/clean operations, but
> then commit d72e9a7a93e4 ("zram: do not use copy_page with non-page
> aligned address") removes the optimization because there's memory
> corruption at that time, the reason was well explained. But after
> commit 1f7319c74275 ("zram: partial IO refactoring"), partial IO uses
> alloc_page() instead of kmalloc to allocate a page, so we can bring
> back the optimization.
> 
> commit 80ba4caf8ba9 ("zram: use copy_page for full page copy") brings
> back partial optimization, missed one point in zram_write_page().
> optimize the full page copying in zram_write_page() with copy_page()
> 
> Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> ---
>  drivers/block/zram/zram_drv.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 3acd7006ad2c..4b2b5098062f 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1478,11 +1478,13 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
>  	dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
>  
>  	src = zstrm->buffer;
> -	if (comp_len == PAGE_SIZE)
> +	if (comp_len == PAGE_SIZE) {
>  		src = kmap_local_page(page);
> -	memcpy(dst, src, comp_len);
> -	if (comp_len == PAGE_SIZE)
> +		copy_page(dst, src);
>  		kunmap_local(src);
> +	} else {
> +		memcpy(dst, src, comp_len);
> +	}

I know this is pre-existing code, but why do we need to kmap
for comp_len == PAGE_SIZE and not for the other cases?  Something
feels really obsfucated here.

Re: [PATCH] zram: use copy_page for full page copy

[Sergey Senozhatsky]

On (24/06/13 22:25), Christoph Hellwig wrote:
> On Thu, Jun 13, 2024 at 08:04:22AM +0800, Jisheng Zhang wrote:
> > commit 42e99bd975fd ("zram: optimize memory operations with
> > clear_page()/copy_page()") optimize page copy/clean operations, but
> > then commit d72e9a7a93e4 ("zram: do not use copy_page with non-page
> > aligned address") removes the optimization because there's memory
> > corruption at that time, the reason was well explained. But after
> > commit 1f7319c74275 ("zram: partial IO refactoring"), partial IO uses
> > alloc_page() instead of kmalloc to allocate a page, so we can bring
> > back the optimization.
> > 
> > commit 80ba4caf8ba9 ("zram: use copy_page for full page copy") brings
> > back partial optimization, missed one point in zram_write_page().
> > optimize the full page copying in zram_write_page() with copy_page()
> > 
> > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > ---
> >  drivers/block/zram/zram_drv.c | 8 +++++---
> >  1 file changed, 5 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> > index 3acd7006ad2c..4b2b5098062f 100644
> > --- a/drivers/block/zram/zram_drv.c
> > +++ b/drivers/block/zram/zram_drv.c
> > @@ -1478,11 +1478,13 @@ static int zram_write_page(struct zram *zram, struct page *page, u32 index)
> >  	dst = zs_map_object(zram->mem_pool, handle, ZS_MM_WO);
> >  
> >  	src = zstrm->buffer;
> > -	if (comp_len == PAGE_SIZE)
> > +	if (comp_len == PAGE_SIZE) {
> >  		src = kmap_local_page(page);
> > -	memcpy(dst, src, comp_len);
> > -	if (comp_len == PAGE_SIZE)
> > +		copy_page(dst, src);
> >  		kunmap_local(src);
> > +	} else {
> > +		memcpy(dst, src, comp_len);
> > +	}
> 
> I know this is pre-existing code, but why do we need to kmap
> for comp_len == PAGE_SIZE and not for the other cases?  Something
> feels really obsfucated here.

It is tricky a little.

If we managed to compress page (size < zsmalloc uncompressible watermark)
then src is per-CPU buffer with compressed data.  Otherwise src is original
page (with uncompressed data).

[PATCH] zram: use copy_page for full page copy

[Mark-PK Tsai]

Some architectures, such as arm, have implemented
optimized copy_page for full page copying.

Replace the full page memcpy with copy_page to
take advantage of the optimization.

Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
---
 drivers/block/zram/zram_drv.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index d77d3664ca08..58700dd73d1d 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1338,7 +1338,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
 	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
 	if (size == PAGE_SIZE) {
 		dst = kmap_atomic(page);
-		memcpy(dst, src, PAGE_SIZE);
+		copy_page(dst, src);
 		kunmap_atomic(dst);
 		ret = 0;
 	} else {
-- 
2.18.0

Re: [PATCH] zram: use copy_page for full page copy

[Sergey Senozhatsky]

On (23/10/07 15:05), Mark-PK Tsai wrote:
> 
> Some architectures, such as arm, have implemented
> optimized copy_page for full page copying.
> 
> Replace the full page memcpy with copy_page to
> take advantage of the optimization.
> 
> Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>

Re: [PATCH] zram: use copy_page for full page copy

[Mark-PK Tsai (蔡沛剛)]

On Sun, 2023-10-08 at 13:38 +0900, Sergey Senozhatsky wrote:
>  	 
> External email : Please do not click links or open attachments until
> you have verified the sender or the content.
>  On (23/10/07 15:05), Mark-PK Tsai wrote:
> > 
> > Some architectures, such as arm, have implemented
> > optimized copy_page for full page copying.
> > 
> > Replace the full page memcpy with copy_page to
> > take advantage of the optimization.
> > 
> > Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
> 
> Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>

I guess this patch may have been overlooked.
Could someone please help to review it?

Thanks,
Mark

Re: [PATCH] zram: use copy_page for full page copy

[Sergey Senozhatsky]

On (24/02/05 06:43), Mark-PK Tsai (蔡沛剛) wrote:
> On Sun, 2023-10-08 at 13:38 +0900, Sergey Senozhatsky wrote:
> >  	 
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> >  On (23/10/07 15:05), Mark-PK Tsai wrote:
> > > 
> > > Some architectures, such as arm, have implemented
> > > optimized copy_page for full page copying.
> > > 
> > > Replace the full page memcpy with copy_page to
> > > take advantage of the optimization.
> > > 
> > > Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
> > 
> > Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>
> 
> I guess this patch may have been overlooked.
> Could someone please help to review it?

Oh, yes. Let me take care of that.

Re: [PATCH] zram: use copy_page for full page copy

[Sergey Senozhatsky]

Cc-ing Andrew on this

On (23/10/07 15:05), Mark-PK Tsai wrote:
> Some architectures, such as arm, have implemented
> optimized copy_page for full page copying.
> 
> Replace the full page memcpy with copy_page to
> take advantage of the optimization.
> 
> Signed-off-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>

Reviewed-by: Sergey Senozhatsky <senozhatsky@chromium.org>

> ---
>  drivers/block/zram/zram_drv.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index d77d3664ca08..58700dd73d1d 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -1338,7 +1338,7 @@ static int zram_read_from_zspool(struct zram *zram, struct page *page,
>  	src = zs_map_object(zram->mem_pool, handle, ZS_MM_RO);
>  	if (size == PAGE_SIZE) {
>  		dst = kmap_atomic(page);
> -		memcpy(dst, src, PAGE_SIZE);
> +		copy_page(dst, src);
>  		kunmap_atomic(dst);
>  		ret = 0;
>  	} else {
> -- 
> 2.18.0