For some case as tun_build_skb() without the needing of using complicated prepare & commit API, add the abort API to abort the operation of page_frag_alloc_*() related API for error handling knowing that no one else is taking extra reference to the just allocated fragment, and add abort_ref API to only abort the reference counting of the allocated fragment if it is already referenced by someone else. CC: Alexander Duyck <alexander.duyck@xxxxxxxxx> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> CC: Linux-MM <linux-mm@xxxxxxxxx> Signed-off-by: Yunsheng Lin <linyunsheng@xxxxxxxxxx> --- Documentation/mm/page_frags.rst | 7 +++++-- include/linux/page_frag_cache.h | 20 ++++++++++++++++++++ mm/page_frag_cache.c | 21 +++++++++++++++++++++ 3 files changed, 46 insertions(+), 2 deletions(-) diff --git a/Documentation/mm/page_frags.rst b/Documentation/mm/page_frags.rst index 34e654c2956e..339e641beb53 100644 --- a/Documentation/mm/page_frags.rst +++ b/Documentation/mm/page_frags.rst @@ -114,9 +114,10 @@ fragsz if there is an alignment requirement for the size of the fragment. .. kernel-doc:: include/linux/page_frag_cache.h :identifiers: page_frag_cache_init page_frag_cache_is_pfmemalloc __page_frag_alloc_align page_frag_alloc_align page_frag_alloc + page_frag_alloc_abort .. kernel-doc:: mm/page_frag_cache.c - :identifiers: page_frag_cache_drain page_frag_free + :identifiers: page_frag_cache_drain page_frag_free page_frag_alloc_abort_ref Coding examples =============== @@ -143,8 +144,10 @@ Allocation & freeing API goto do_error; err = do_something(va, size); - if (err) + if (err) { + page_frag_alloc_abort(nc, va, size); goto do_error; + } ... diff --git a/include/linux/page_frag_cache.h b/include/linux/page_frag_cache.h index a2b1127e8ac8..c3347c97522c 100644 --- a/include/linux/page_frag_cache.h +++ b/include/linux/page_frag_cache.h @@ -141,5 +141,25 @@ static inline void *page_frag_alloc(struct page_frag_cache *nc, } void page_frag_free(void *addr); +void page_frag_alloc_abort_ref(struct page_frag_cache *nc, void *va, + unsigned int fragsz); + +/** + * page_frag_alloc_abort - Abort the page fragment allocation. + * @nc: page_frag cache to which the page fragment is aborted back + * @va: virtual address of page fragment to be aborted + * @fragsz: size of the page fragment to be aborted + * + * It is expected to be called from the same context as the allocation API. + * Mostly used for error handling cases to abort the fragment allocation knowing + * that no one else is taking extra reference to the just aborted fragment, so + * that the aborted fragment can be reused. + */ +static inline void page_frag_alloc_abort(struct page_frag_cache *nc, void *va, + unsigned int fragsz) +{ + page_frag_alloc_abort_ref(nc, va, fragsz); + nc->offset -= fragsz; +} #endif diff --git a/mm/page_frag_cache.c b/mm/page_frag_cache.c index d014130fb893..4d5626da42ed 100644 --- a/mm/page_frag_cache.c +++ b/mm/page_frag_cache.c @@ -201,3 +201,24 @@ void page_frag_free(void *addr) free_unref_page(page, compound_order(page)); } EXPORT_SYMBOL(page_frag_free); + +/** + * page_frag_alloc_abort_ref - Abort the reference of allocated fragment. + * @nc: page_frag cache to which the page fragment is aborted back + * @va: virtual address of page fragment to be aborted + * @fragsz: size of the page fragment to be aborted + * + * It is expected to be called from the same context as the allocation API. + * Mostly used for error handling cases to abort the reference of allocated + * fragment if the fragment has been referenced for other usages, to aovid the + * atomic operation of page_frag_free() API. + */ +void page_frag_alloc_abort_ref(struct page_frag_cache *nc, void *va, + unsigned int fragsz) +{ + VM_BUG_ON(va + fragsz != + encoded_page_decode_virt(nc->encoded_page) + nc->offset); + + nc->pagecnt_bias++; +} +EXPORT_SYMBOL(page_frag_alloc_abort_ref); -- 2.33.0