| Message ID | 20240613000422.1918-1-jszhang@kernel.org (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | zram: use copy_page for full page copy | expand |
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)?
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.
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.
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).
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);
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(-)