| Message ID | 20231213-zswap-dstmem-v2-1-daa5d9ae41a7@bytedance.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm/zswap: dstmem reuse optimizations and cleanups | expand |
Acked-by: Chris Li <chrisl@kernel.org> (Google) Chris On Mon, Dec 18, 2023 at 12:22 AM Chengming Zhou <zhouchengming@bytedance.com> wrote: > > Change the dstmem size from 2 * PAGE_SIZE to only one page since > we only need at most one page when compress, and the "dlen" is also > PAGE_SIZE in acomp_request_set_params(). If the output size > PAGE_SIZE > we don't wanna store the output in zswap anyway. > > So change it to one page, and delete the stale comment. > > There is no any history about the reason why we needed 2 pages, it has > been 2 * PAGE_SIZE since the time zswap was first merged. > > According to Yosry and Nhat, one potential reason is that we used to > store a zswap header containing the swap entry in the compressed page > for writeback purposes, but we don't do that anymore. > > This patch works good in kernel build testing even when the input data > doesn't compress at all (i.e. dlen == PAGE_SIZE), which we can see > from the bpftrace tool: > > bpftrace -e 'k:zpool_malloc {@[(uint32)arg1==4096]=count()}' > @[1]: 2 > @[0]: 12011430 > > Reviewed-by: Yosry Ahmed <yosryahmed@google.com> > Reviewed-by: Nhat Pham <nphamcs@gmail.com> > Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> > --- > mm/zswap.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/mm/zswap.c b/mm/zswap.c > index 7ee54a3d8281..976f278aa507 100644 > --- a/mm/zswap.c > +++ b/mm/zswap.c > @@ -707,7 +707,7 @@ static int zswap_dstmem_prepare(unsigned int cpu) > struct mutex *mutex; > u8 *dst; > > - dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu)); > + dst = kmalloc_node(PAGE_SIZE, GFP_KERNEL, cpu_to_node(cpu)); > if (!dst) > return -ENOMEM; > > @@ -1662,8 +1662,7 @@ bool zswap_store(struct folio *folio) > sg_init_table(&input, 1); > sg_set_page(&input, page, PAGE_SIZE, 0); > > - /* zswap_dstmem is of size (PAGE_SIZE * 2). Reflect same in sg_list */ > - sg_init_one(&output, dst, PAGE_SIZE * 2); > + sg_init_one(&output, dst, PAGE_SIZE); > acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen); > /* > * it maybe looks a little bit silly that we send an asynchronous request, > > -- > b4 0.10.1
diff --git a/mm/zswap.c b/mm/zswap.c index 7ee54a3d8281..976f278aa507 100644 --- a/mm/zswap.c +++ b/mm/zswap.c @@ -707,7 +707,7 @@ static int zswap_dstmem_prepare(unsigned int cpu) struct mutex *mutex; u8 *dst; - dst = kmalloc_node(PAGE_SIZE * 2, GFP_KERNEL, cpu_to_node(cpu)); + dst = kmalloc_node(PAGE_SIZE, GFP_KERNEL, cpu_to_node(cpu)); if (!dst) return -ENOMEM; @@ -1662,8 +1662,7 @@ bool zswap_store(struct folio *folio) sg_init_table(&input, 1); sg_set_page(&input, page, PAGE_SIZE, 0); - /* zswap_dstmem is of size (PAGE_SIZE * 2). Reflect same in sg_list */ - sg_init_one(&output, dst, PAGE_SIZE * 2); + sg_init_one(&output, dst, PAGE_SIZE); acomp_request_set_params(acomp_ctx->req, &input, &output, PAGE_SIZE, dlen); /* * it maybe looks a little bit silly that we send an asynchronous request,
Change the dstmem size from 2 * PAGE_SIZE to only one page since we only need at most one page when compress, and the "dlen" is also PAGE_SIZE in acomp_request_set_params(). If the output size > PAGE_SIZE we don't wanna store the output in zswap anyway. So change it to one page, and delete the stale comment. There is no any history about the reason why we needed 2 pages, it has been 2 * PAGE_SIZE since the time zswap was first merged. According to Yosry and Nhat, one potential reason is that we used to store a zswap header containing the swap entry in the compressed page for writeback purposes, but we don't do that anymore. This patch works good in kernel build testing even when the input data doesn't compress at all (i.e. dlen == PAGE_SIZE), which we can see from the bpftrace tool: bpftrace -e 'k:zpool_malloc {@[(uint32)arg1==4096]=count()}' @[1]: 2 @[0]: 12011430 Reviewed-by: Yosry Ahmed <yosryahmed@google.com> Reviewed-by: Nhat Pham <nphamcs@gmail.com> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> --- mm/zswap.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-)