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charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.48.4 (3.48.4-1.fc38) MIME-Version: 1.0 X-Rspam-User: X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 81C6B20002 X-Stat-Signature: dsz3c6o9nms63z79rxbje5ws66kpxi69 X-HE-Tag: 1712512357-629219 X-HE-Meta: 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 AevmnNth GGkjDE3ftglcXN8htBdF9qHGPzf4ywHZNfdZchyOVIQPcdHiRAty2uE/3nG+yfX5f8FONvPHpidGATg9DHNDLOl9pe1ak3oSeb7wXYNpU1gLZyNZ7UOmi+Z0Khf3nviQjd1tZXnPPy+Zp82e6XJXJQyZ1Og== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Sun, 2024-04-07 at 21:08 +0800, Yunsheng Lin wrote: > We are above to use page_frag_alloc_*() API to not just > allocate memory for skb->data, but also use them to do > the memory allocation for skb frag too. Currently the > implementation of page_frag in mm subsystem is running > the offset as a countdown rather than count-up value, > there may have several advantages to that as mentioned > in [1], but it may have some disadvantages, for example, > it may disable skb frag coaleasing and more correct cache > prefetching >=20 > We have a trade-off to make in order to have a unified > implementation and API for page_frag, so use a initial zero > offset in this patch, and the following patch will try to > make some optimization to aovid the disadvantages as much > as possible. >=20 > 1. https://lore.kernel.org/all/f4abe71b3439b39d17a6fb2d410180f367cadf5c.c= amel@gmail.com/ >=20 > CC: Alexander Duyck > Signed-off-by: Yunsheng Lin > --- > mm/page_frag_cache.c | 31 ++++++++++++++----------------- > 1 file changed, 14 insertions(+), 17 deletions(-) >=20 > diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c > index a0f90ba25200..3e3e88d9af90 100644 > --- a/mm/page_frag_cache.c > +++ b/mm/page_frag_cache.c > @@ -67,9 +67,8 @@ void *__page_frag_alloc_align(struct page_frag_cache *n= c, > unsigned int fragsz, gfp_t gfp_mask, > unsigned int align_mask) > { > - unsigned int size =3D PAGE_SIZE; > + unsigned int size, offset; > struct page *page; > - int offset; > =20 > if (unlikely(!nc->va)) { > refill: > @@ -77,10 +76,6 @@ void *__page_frag_alloc_align(struct page_frag_cache *= nc, > if (!page) > return NULL; > =20 > -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > - /* if size can vary use size else just use PAGE_SIZE */ > - size =3D nc->size; > -#endif > /* Even if we own the page, we do not use atomic_set(). > * This would break get_page_unless_zero() users. > */ > @@ -89,11 +84,18 @@ void *__page_frag_alloc_align(struct page_frag_cache = *nc, > /* reset page count bias and offset to start of new frag */ > nc->pfmemalloc =3D page_is_pfmemalloc(page); > nc->pagecnt_bias =3D PAGE_FRAG_CACHE_MAX_SIZE + 1; > - nc->offset =3D size; > + nc->offset =3D 0; > } > =20 > - offset =3D nc->offset - fragsz; > - if (unlikely(offset < 0)) { > +#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > + /* if size can vary use size else just use PAGE_SIZE */ > + size =3D nc->size; > +#else > + size =3D PAGE_SIZE; > +#endif > + > + offset =3D ALIGN(nc->offset, -align_mask); > + if (unlikely(offset + fragsz > size)) { Rather than using "ALIGN" with a negative value it would probably make more sense to use __ALIGN_KERNEL_MASK with ~align_mask. I am not sure how well the compiler sorts out the use of negatives to flip values that are then converted to masks with the "(a) - 1". > page =3D virt_to_page(nc->va); > =20 > if (!page_ref_sub_and_test(page, nc->pagecnt_bias)) > @@ -104,17 +106,13 @@ void *__page_frag_alloc_align(struct page_frag_cach= e *nc, > goto refill; > } > =20 > -#if (PAGE_SIZE < PAGE_FRAG_CACHE_MAX_SIZE) > - /* if size can vary use size else just use PAGE_SIZE */ > - size =3D nc->size; > -#endif > /* OK, page count is 0, we can safely set it */ > set_page_count(page, PAGE_FRAG_CACHE_MAX_SIZE + 1); > =20 > /* reset page count bias and offset to start of new frag */ > nc->pagecnt_bias =3D PAGE_FRAG_CACHE_MAX_SIZE + 1; > - offset =3D size - fragsz; > - if (unlikely(offset < 0)) { > + offset =3D 0; > + if (unlikely(fragsz > size)) { > /* > * The caller is trying to allocate a fragment > * with fragsz > PAGE_SIZE but the cache isn't big > @@ -129,8 +127,7 @@ void *__page_frag_alloc_align(struct page_frag_cache = *nc, > } > =20 > nc->pagecnt_bias--; > - offset &=3D align_mask; > - nc->offset =3D offset; > + nc->offset =3D offset + fragsz; > =20 > return nc->va + offset; > }