| Message ID | 20241113152442.4000468-12-aleksander.lobakin@intel.com (mailing list archive) |
|---|---|
| State | Changes Requested |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | xdp: a fistful of generic changes (+libeth_xdp) | expand |
On Wed, Nov 13, 2024 at 04:24:34PM +0100, Alexander Lobakin wrote: > The code piece which would attach a frag to &xdp_buff is almost > identical across the drivers supporting XDP multi-buffer on Rx. Yes, I was reviewing such a change when I noticed your patch. We will use this helper instead. Thanks! > Make it a generic elegant "oneliner". > Also, I see lots of drivers calculating frags_truesize as > `xdp->frame_sz * nr_frags`. I can't say this is fully correct, since > frags might be backed by chunks of different sizes, especially with > stuff like the header split. Even page_pool_alloc() can give you two > different truesizes on two subsequent requests to allocate the same > buffer size. Add a field to &skb_shared_info (unionized as there's no > free slot currently on x86_64) to track the "true" truesize. It can > be used later when updating an skb. > > Reviewed-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com> > Signed-off-by: Alexander Lobakin <aleksander.lobakin@intel.com> Reviewed-by: Ido Schimmel <idosch@nvidia.com>
On Wed, 13 Nov 2024 16:24:34 +0100 Alexander Lobakin wrote: > +static inline bool __xdp_buff_add_frag(struct xdp_buff *xdp, struct page *page, > + u32 offset, u32 size, u32 truesize, > + bool try_coalesce) > +{ > + struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp); > + skb_frag_t *prev; > + u32 nr_frags; > + > + if (!xdp_buff_has_frags(xdp)) { > + xdp_buff_set_frags_flag(xdp); > + > + nr_frags = 0; > + sinfo->xdp_frags_size = 0; > + sinfo->xdp_frags_truesize = 0; > + > + goto fill; > + } > + > + nr_frags = sinfo->nr_frags; > + if (unlikely(nr_frags == MAX_SKB_FRAGS)) > + return false; > + > + prev = &sinfo->frags[nr_frags - 1]; > + if (try_coalesce && page == skb_frag_page(prev) && > + offset == skb_frag_off(prev) + skb_frag_size(prev)) > + skb_frag_size_add(prev, size); don't we have to release the reference if we coalesced? > + else > +fill: > + __skb_fill_page_desc_noacc(sinfo, nr_frags++, page, > + offset, size); > + > + sinfo->nr_frags = nr_frags; > + sinfo->xdp_frags_size += size; > + sinfo->xdp_frags_truesize += truesize; > + > + return true; > +}
From: Jakub Kicinski <kuba@kernel.org> Date: Fri, 15 Nov 2024 18:40:59 -0800 > On Wed, 13 Nov 2024 16:24:34 +0100 Alexander Lobakin wrote: >> +static inline bool __xdp_buff_add_frag(struct xdp_buff *xdp, struct page *page, >> + u32 offset, u32 size, u32 truesize, >> + bool try_coalesce) >> +{ >> + struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp); >> + skb_frag_t *prev; >> + u32 nr_frags; >> + >> + if (!xdp_buff_has_frags(xdp)) { >> + xdp_buff_set_frags_flag(xdp); >> + >> + nr_frags = 0; >> + sinfo->xdp_frags_size = 0; >> + sinfo->xdp_frags_truesize = 0; >> + >> + goto fill; >> + } >> + >> + nr_frags = sinfo->nr_frags; >> + if (unlikely(nr_frags == MAX_SKB_FRAGS)) >> + return false; >> + >> + prev = &sinfo->frags[nr_frags - 1]; >> + if (try_coalesce && page == skb_frag_page(prev) && >> + offset == skb_frag_off(prev) + skb_frag_size(prev)) >> + skb_frag_size_add(prev, size); > > don't we have to release the reference if we coalesced? Correct. I realized that when replying to Ido =\ > >> + else >> +fill: >> + __skb_fill_page_desc_noacc(sinfo, nr_frags++, page, >> + offset, size); >> + >> + sinfo->nr_frags = nr_frags; >> + sinfo->xdp_frags_size += size; >> + sinfo->xdp_frags_truesize += truesize; >> + >> + return true; >> +} Thanks, Olek
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 92f1d1e218b5..f4fe699248a2 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -608,11 +608,19 @@ struct skb_shared_info { * Warning : all fields before dataref are cleared in __alloc_skb() */ atomic_t dataref; - unsigned int xdp_frags_size; - /* Intermediate layers must ensure that destructor_arg - * remains valid until skb destructor */ - void * destructor_arg; + union { + struct { + u32 xdp_frags_size; + u32 xdp_frags_truesize; + }; + + /* + * Intermediate layers must ensure that destructor_arg + * remains valid until skb destructor. + */ + void *destructor_arg; + }; /* must be last field, see pskb_expand_head() */ skb_frag_t frags[MAX_SKB_FRAGS]; diff --git a/include/net/xdp.h b/include/net/xdp.h index d33d73e798fe..4c19042adf80 100644 --- a/include/net/xdp.h +++ b/include/net/xdp.h @@ -167,6 +167,88 @@ xdp_get_buff_len(const struct xdp_buff *xdp) return len; } +/** + * __xdp_buff_add_frag - attach a frag to an &xdp_buff + * @xdp: XDP buffer to attach the frag to + * @page: page containing the frag + * @offset: page offset at which the frag starts + * @size: size of the frag + * @truesize: truesize (page / page frag size) of the frag + * @try_coalesce: whether to try coalescing the frags + * + * Attach a frag to an XDP buffer. If it currently has no frags attached, + * initialize the related fields, otherwise check that the frag number + * didn't reach the limit of ``MAX_SKB_FRAGS``. If possible, try coalescing + * the frag with the previous one. + * The function doesn't check/update the pfmemalloc bit. Please use the + * non-underscored wrapper in drivers. + * + * Return: true on success, false if there's no space for the frag in + * the shared info struct. + */ +static inline bool __xdp_buff_add_frag(struct xdp_buff *xdp, struct page *page, + u32 offset, u32 size, u32 truesize, + bool try_coalesce) +{ + struct skb_shared_info *sinfo = xdp_get_shared_info_from_buff(xdp); + skb_frag_t *prev; + u32 nr_frags; + + if (!xdp_buff_has_frags(xdp)) { + xdp_buff_set_frags_flag(xdp); + + nr_frags = 0; + sinfo->xdp_frags_size = 0; + sinfo->xdp_frags_truesize = 0; + + goto fill; + } + + nr_frags = sinfo->nr_frags; + if (unlikely(nr_frags == MAX_SKB_FRAGS)) + return false; + + prev = &sinfo->frags[nr_frags - 1]; + if (try_coalesce && page == skb_frag_page(prev) && + offset == skb_frag_off(prev) + skb_frag_size(prev)) + skb_frag_size_add(prev, size); + else +fill: + __skb_fill_page_desc_noacc(sinfo, nr_frags++, page, + offset, size); + + sinfo->nr_frags = nr_frags; + sinfo->xdp_frags_size += size; + sinfo->xdp_frags_truesize += truesize; + + return true; +} + +/** + * xdp_buff_add_frag - attach a frag to an &xdp_buff + * @xdp: XDP buffer to attach the frag to + * @page: page containing the frag + * @offset: page offset at which the frag starts + * @size: size of the frag + * @truesize: truesize (page / page frag size) of the frag + * + * Version of __xdp_buff_add_frag() which takes care of the pfmemalloc bit. + * + * Return: true on success, false if there's no space for the frag in + * the shared info struct. + */ +static inline bool xdp_buff_add_frag(struct xdp_buff *xdp, struct page *page, + u32 offset, u32 size, u32 truesize) +{ + if (!__xdp_buff_add_frag(xdp, page, offset, size, truesize, true)) + return false; + + if (unlikely(page_is_pfmemalloc(page))) + xdp_buff_set_frag_pfmemalloc(xdp); + + return true; +} + struct xdp_frame { void *data; u32 len; @@ -230,7 +312,13 @@ xdp_update_skb_shared_info(struct sk_buff *skb, u8 nr_frags, unsigned int size, unsigned int truesize, bool pfmemalloc) { - skb_shinfo(skb)->nr_frags = nr_frags; + struct skb_shared_info *sinfo = skb_shinfo(skb); + + sinfo->nr_frags = nr_frags; + /* ``destructor_arg`` is unionized with ``xdp_frags_{,true}size``, + * reset it after that these fields aren't used anymore. + */ + sinfo->destructor_arg = NULL; skb->len += size; skb->data_len += size;