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This is a preparatory change made for shmem_fadvise() functionality in the next patch. No functional changes in this patch. Signed-off-by: Charan Teja Kalla --- mm/fadvise.c | 11 +---------- mm/internal.h | 21 +++++++++++++++++++++ 2 files changed, 22 insertions(+), 10 deletions(-) diff --git a/mm/fadvise.c b/mm/fadvise.c index bf04fec..10169c6 100644 --- a/mm/fadvise.c +++ b/mm/fadvise.c @@ -65,16 +65,7 @@ int generic_fadvise(struct file *file, loff_t offset, loff_t len, int advice) return 0; } - /* - * Careful about overflows. Len == 0 means "as much as possible". Use - * unsigned math because signed overflows are undefined and UBSan - * complains. - */ - endbyte = (u64)offset + (u64)len; - if (!len || endbyte < len) - endbyte = LLONG_MAX; - else - endbyte--; /* inclusive */ + endbyte = fadvise_calc_endbyte(offset, len); switch (advice) { case POSIX_FADV_NORMAL: diff --git a/mm/internal.h b/mm/internal.h index bcf75a8..47858af 100644 --- a/mm/internal.h +++ b/mm/internal.h @@ -637,6 +637,27 @@ static inline void vunmap_range_noflush(unsigned long start, unsigned long end) } #endif /* !CONFIG_MMU */ +/* + * Helper function to get the endbyte of a file that fadvise can operate on. + */ +static inline loff_t fadvise_calc_endbyte(loff_t offset, loff_t len) +{ + loff_t endbyte; + + /* + * Careful about overflows. Len == 0 means "as much as possible". Use + * unsigned math because signed overflows are undefined and UBSan + * complains. + */ + endbyte = (u64)offset + (u64)len; + if (!len || endbyte < len) + endbyte = LLONG_MAX; + else + endbyte--; /* inclusive */ + + return endbyte; +} + /* Memory initialisation debug and verification */ enum mminit_level { MMINIT_WARNING, From patchwork Mon Feb 6 14:21:33 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Charan Teja Kalla X-Patchwork-Id: 53318 Return-Path: Delivered-To: ouuuleilei@gmail.com Received: by 2002:adf:eb09:0:0:0:0:0 with SMTP id s9csp2269183wrn; Mon, 6 Feb 2023 06:35:35 -0800 (PST) X-Google-Smtp-Source: AK7set+LHBS/BL7cA+h/rHmr2Pmd3eyB3DLwSW8jORhaaDTn7jUca09iQmDprA3ip0CvUYPHgmLT X-Received: by 2002:a17:902:e5d2:b0:199:14d2:5e26 with SMTP id u18-20020a170902e5d200b0019914d25e26mr4840688plf.1.1675694135440; Mon, 06 Feb 2023 06:35:35 -0800 (PST) ARC-Seal: i=1; a=rsa-sha256; t=1675694135; cv=none; d=google.com; s=arc-20160816; b=GNATIOsQ4cJxAYV4N6b50POF8ZCfJwlVntCspxkAUV8GR3wb1nTEmHC8dbeR/e5+/r 0U+Yq8J/4g8MI0HsFWCvnb2+TH+RdSydfGe7W83KMThV3e5GhoSk+3tP9hZbcTuIFS5J yEEKMCtqUECakynWqxzYE12mxWR2W5afAR/MFTW7BZ8fwuutLW2vcSkvWZxCpOz8gUv0 EeOijKVDLuizb4Npfg9LcsIGDeYMXV6HbR60OSx0R+f6K7gWFpfh8n0k+f5WulDqZxmd ktMVD6CsVe71gLssLHxx2xFLkQdWdTaftL5jmfZArjwwHUsw4yLNwj1s1uguBmd19cX8 wYlA== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=list-id:precedence:mime-version:references:in-reply-to:message-id :date:subject:cc:to:from:dkim-signature; bh=8pVCKR95UYar7CDkFZyHmi085Ldot0hMkd4M0rzUh9s=; b=rzsWhKBW9kkGM4rKE0bWaanztvU/xWlACV+joJitFTl52I90GirTLZKFJYqi08hq7v 8z4aR6CLRf+/4+H5dZ1aEpbODBYEoYJgtnScalXI8tRYDVHlp72W5N8zhcMulSeTJQtb 8uE5H2ADudxDpe3G6ERIthVhTtKuM8l0dfACJsqTkh342ke1hsJB/Y6IN4pK0T0rgfv1 dvzYEq3ETHzaRsi3IGn7dL0tKZjcS/sWS7NiishgsxTeNX7VwBYIyZ2rbxhggsklDvjE enjworT118Ib8VPkIXBp/iqt1sSlhKEDrdK3USl5iF7AEacFdJU9A0Ynwo00sijndaXs 8cZQ== ARC-Authentication-Results: i=1; mx.google.com; dkim=pass header.i=@quicinc.com header.s=qcppdkim1 header.b=BSXLzf2M; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=quicinc.com Received: from out1.vger.email (out1.vger.email. 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But then there is file_operations->fadvise() that lets the file systems to implement their own fadvise implementation. Use this support to implement some of the POSIX_FADV_XXX functionality for shmem files. This patch aims to implement POSIX_FADV_WILLNEED and POSIX_FADV_DONTNEED advices to shmem files which can be helpful for the clients who may want to manage the shmem pages of the files that are created through shmem_file_setup[_with_mnt](). One usecase is implemented on the Snapdragon SoC's running Android where the graphics client is allocating lot of shmem pages per process and pinning them. When this process is put to background, the instantaneous reclaim is performed on those shmem pages using the logic implemented downstream[3][4]. With this patch, the client can now issue the fadvise calls on the shmem files that does the instantaneous reclaim which can aid the use cases like mentioned above. This usecase lead to ~2% reduction in average launch latencies of the apps and 10% in total number of kills by the low memory killer running on Android. Some questions asked while reviewing this patch: Q) Can the same thing be achieved with FD mapped to user and use madvise? A) All drivers are not mapping all the shmem fd's to user space and want to manage them with in the kernel. Ex: shmem memory can be mapped to the other subsystems and they fill in the data and then give it to other subsystem for further processing, where, the user mapping is not at all required. A simple example, memory that is given for gpu subsystem which can be filled directly and give to display subsystem. And the respective drivers know well about when to keep that memory in ram or swap based on may be a user activity. Q) Should we add the documentation section in Manual pages? A) The man[1] pages for the fadvise() whatever says is also applicable for shmem files. so couldn't feel it correct to add specific to shmem files separately. Q) The proposed semantics of POSIX_FADV_DONTNEED is actually similar to MADV_PAGEOUT and different from MADV_DONTNEED. This is a user facing API and this difference will cause confusion? A) man pages [2] says that "POSIX_FADV_DONTNEED attempts to free cached pages associated with the specified region." This means on issuing this FADV, it is expected to free the file cache pages. And it is implementation defined If the dirty pages may be attempted to writeback. And the unwritten dirty pages will not be freed. So, FADV_DONTNEED also covers the semantics of MADV_PAGEOUT for file pages and there is no purpose of PAGEOUT for file pages. [1] https://linux.die.net/man/2/fadvise [2] https://man7.org/linux/man-pages/man2/posix_fadvise.2.html [3] https://git.codelinaro.org/clo/la/platform/vendor/qcom/opensource/graphics-kernel/-/blob/gfx-kernel.lnx.1.0.r3-rel/kgsl_reclaim.c#L289 [4] https://android.googlesource.com/kernel/common/+/refs/heads/android12-5.10/mm/shmem.c#4310 Signed-off-by: Charan Teja Kalla --- mm/shmem.c | 115 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 115 insertions(+) diff --git a/mm/shmem.c b/mm/shmem.c index 0005ab2..58aa3d7 100644 --- a/mm/shmem.c +++ b/mm/shmem.c @@ -39,6 +39,9 @@ #include #include #include +#include +#include +#include #include "swap.h" static struct vfsmount *shm_mnt; @@ -2327,6 +2330,117 @@ static void shmem_set_inode_flags(struct inode *inode, unsigned int fsflags) #define shmem_initxattrs NULL #endif +static void shmem_isolate_pages_range(struct address_space *mapping, loff_t start, + loff_t end, struct list_head *list) +{ + XA_STATE(xas, &mapping->i_pages, start); + struct folio *folio; + + rcu_read_lock(); + xas_for_each(&xas, folio, end) { + if (xas_retry(&xas, folio)) + continue; + if (xa_is_value(folio)) + continue; + + if (!folio_try_get(folio)) + continue; + if (folio_test_unevictable(folio) || folio_mapped(folio) || + folio_isolate_lru(folio)) { + folio_put(folio); + continue; + } + folio_put(folio); + + /* + * Prepare the page to be passed to the reclaim_pages(). + * VM couldn't reclaim the page unless we clear PG_young. + */ + folio_clear_referenced(folio); + folio_test_clear_young(folio); + list_add(&folio->lru, list); + if (need_resched()) { + xas_pause(&xas); + cond_resched_rcu(); + } + } + rcu_read_unlock(); +} + +static int shmem_fadvise_dontneed(struct address_space *mapping, loff_t start, + loff_t end) +{ + LIST_HEAD(folio_list); + + if (!total_swap_pages) + return 0; + + lru_add_drain(); + shmem_isolate_pages_range(mapping, start, end, &folio_list); + reclaim_pages(&folio_list); + + return 0; +} + +static int shmem_fadvise_willneed(struct address_space *mapping, + pgoff_t start, pgoff_t long end) +{ + struct page *page; + pgoff_t index; + + xa_for_each_range(&mapping->i_pages, index, page, start, end) { + if (!xa_is_value(page)) + continue; + page = shmem_read_mapping_page(mapping, index); + if (!IS_ERR(page)) + put_page(page); + } + + return 0; +} + +static int shmem_fadvise(struct file *file, loff_t offset, loff_t len, int advice) +{ + loff_t endbyte; + pgoff_t start_index; + pgoff_t end_index; + struct address_space *mapping; + struct inode *inode = file_inode(file); + int ret = 0; + + if (S_ISFIFO(inode->i_mode)) + return -ESPIPE; + + mapping = file->f_mapping; + if (!mapping || len < 0 || !shmem_mapping(mapping)) + return -EINVAL; + + endbyte = fadvise_calc_endbyte(offset, len); + + start_index = offset >> PAGE_SHIFT; + end_index = endbyte >> PAGE_SHIFT; + switch (advice) { + case POSIX_FADV_DONTNEED: + ret = shmem_fadvise_dontneed(mapping, start_index, end_index); + break; + case POSIX_FADV_WILLNEED: + ret = shmem_fadvise_willneed(mapping, start_index, end_index); + break; + case POSIX_FADV_NORMAL: + case POSIX_FADV_RANDOM: + case POSIX_FADV_SEQUENTIAL: + case POSIX_FADV_NOREUSE: + /* + * No bad return value, but ignore advice. + */ + break; + default: + return -EINVAL; + } + + return ret; +} + static struct inode *shmem_get_inode(struct super_block *sb, struct inode *dir, umode_t mode, dev_t dev, unsigned long flags) { @@ -3933,6 +4047,7 @@ static const struct file_operations shmem_file_operations = { .splice_write = iter_file_splice_write, .fallocate = shmem_fallocate, #endif + .fadvise = shmem_fadvise, }; static const struct inode_operations shmem_inode_operations = {