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Message-ID: <85f41db3-8d64-240a-7876-9f3b3dea29cb@huawei.com>
Date: Wed, 9 Dec 2020 18:07:08 +0800
From: Chao Yu <yuchao0@...wei.com>
To: Gao Xiang <hsiangkao@....com>, <linux-erofs@...ts.ozlabs.org>
CC: LKML <linux-kernel@...r.kernel.org>, Chao Yu <chao@...nel.org>,
Gao Xiang <hsiangkao@...hat.com>
Subject: Re: [PATCH] erofs: force inplace I/O under low memory scenario
On 2020/12/8 13:46, Gao Xiang wrote:
> From: Gao Xiang <hsiangkao@...hat.com>
>
> Try to forcely switch to inplace I/O under low memory scenario in
> order to avoid direct memory reclaim due to cached page allocation.
>
> Signed-off-by: Gao Xiang <hsiangkao@...hat.com>
> ---
> This was commercially used internally for years, but due to customized
> page->mapping before, it cannot cleanly upstream till now. Since magical
> page->mapping is now gone, adapt this to the latest dev branch for
> better low-memory performance (fully use inplace I/O instead.)
>
> fs/erofs/compress.h | 3 +++
> fs/erofs/zdata.c | 49 +++++++++++++++++++++++++++++++++++++--------
> 2 files changed, 44 insertions(+), 8 deletions(-)
>
> diff --git a/fs/erofs/compress.h b/fs/erofs/compress.h
> index 2bbf47f353ef..c51a741a1232 100644
> --- a/fs/erofs/compress.h
> +++ b/fs/erofs/compress.h
> @@ -27,11 +27,13 @@ struct z_erofs_decompress_req {
> };
>
> #define Z_EROFS_SHORTLIVED_PAGE (-1UL << 2)
> +#define Z_EROFS_PREALLOCATED_PAGE (-2UL << 2)
>
> /*
> * For all pages in a pcluster, page->private should be one of
> * Type Last 2bits page->private
> * short-lived page 00 Z_EROFS_SHORTLIVED_PAGE
> + * preallocated page (tryalloc) 00 Z_EROFS_PREALLOCATED_PAGE
> * cached/managed page 00 pointer to z_erofs_pcluster
> * online page (file-backed, 01/10/11 sub-index << 2 | count
> * some pages can be used for inplace I/O)
> @@ -39,6 +41,7 @@ struct z_erofs_decompress_req {
> * page->mapping should be one of
> * Type page->mapping
> * short-lived page NULL
> + * preallocated page NULL
> * cached/managed page non-NULL or NULL (invalidated/truncated page)
> * online page non-NULL
> *
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index b1b6cd03046f..b84e6a2fb00c 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -20,6 +20,11 @@
> enum z_erofs_cache_alloctype {
> DONTALLOC, /* don't allocate any cached pages */
> DELAYEDALLOC, /* delayed allocation (at the time of submitting io) */
> + /*
> + * try to use cached I/O if page allocation succeeds or fallback
> + * to in-place I/O instead to avoid any direct reclaim.
> + */
> + TRYALLOC,
> };
>
> /*
> @@ -154,13 +159,15 @@ static DEFINE_MUTEX(z_pagemap_global_lock);
>
> static void preload_compressed_pages(struct z_erofs_collector *clt,
> struct address_space *mc,
> - enum z_erofs_cache_alloctype type)
> + enum z_erofs_cache_alloctype type,
> + struct list_head *pagepool)
> {
> const struct z_erofs_pcluster *pcl = clt->pcl;
> const unsigned int clusterpages = BIT(pcl->clusterbits);
> struct page **pages = clt->compressedpages;
> pgoff_t index = pcl->obj.index + (pages - pcl->compressed_pages);
> bool standalone = true;
> + gfp_t gfp = mapping_gfp_constraint(mc, GFP_KERNEL) & ~__GFP_DIRECT_RECLAIM;
Could be local as there is only one place uses it.
Reviewed-by: Chao Yu <yuchao0@...wei.com>
Thanks,
>
> if (clt->mode < COLLECT_PRIMARY_FOLLOWED)
> return;
> @@ -168,6 +175,7 @@ static void preload_compressed_pages(struct z_erofs_collector *clt,
> for (; pages < pcl->compressed_pages + clusterpages; ++pages) {
> struct page *page;
> compressed_page_t t;
> + struct page *newpage = NULL;
>
> /* the compressed page was loaded before */
> if (READ_ONCE(*pages))
> @@ -179,7 +187,17 @@ static void preload_compressed_pages(struct z_erofs_collector *clt,
> t = tag_compressed_page_justfound(page);
> } else if (type == DELAYEDALLOC) {
> t = tagptr_init(compressed_page_t, PAGE_UNALLOCATED);
> + } else if (type == TRYALLOC) {
> + gfp |= __GFP_NOMEMALLOC | __GFP_NORETRY | __GFP_NOWARN;
> +
> + newpage = erofs_allocpage(pagepool, gfp);
> + if (!newpage)
> + goto dontalloc;
> +
> + set_page_private(newpage, Z_EROFS_PREALLOCATED_PAGE);
> + t = tag_compressed_page_justfound(newpage);
> } else { /* DONTALLOC */
> +dontalloc:
> if (standalone)
> clt->compressedpages = pages;
> standalone = false;
> @@ -189,8 +207,12 @@ static void preload_compressed_pages(struct z_erofs_collector *clt,
> if (!cmpxchg_relaxed(pages, NULL, tagptr_cast_ptr(t)))
> continue;
>
> - if (page)
> + if (page) {
> put_page(page);
> + } else if (newpage) {
> + set_page_private(newpage, 0);
> + list_add(&newpage->lru, pagepool);
> + }
> }
>
> if (standalone) /* downgrade to PRIMARY_FOLLOWED_NOINPLACE */
> @@ -560,7 +582,7 @@ static bool should_alloc_managed_pages(struct z_erofs_decompress_frontend *fe,
> }
>
> static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
> - struct page *page)
> + struct page *page, struct list_head *pagepool)
> {
> struct inode *const inode = fe->inode;
> struct erofs_sb_info *const sbi = EROFS_I_SB(inode);
> @@ -613,11 +635,12 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
>
> /* preload all compressed pages (maybe downgrade role if necessary) */
> if (should_alloc_managed_pages(fe, sbi->ctx.cache_strategy, map->m_la))
> - cache_strategy = DELAYEDALLOC;
> + cache_strategy = TRYALLOC;
> else
> cache_strategy = DONTALLOC;
>
> - preload_compressed_pages(clt, MNGD_MAPPING(sbi), cache_strategy);
> + preload_compressed_pages(clt, MNGD_MAPPING(sbi),
> + cache_strategy, pagepool);
>
> hitted:
> /*
> @@ -1011,6 +1034,16 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
> justfound = tagptr_unfold_tags(t);
> page = tagptr_unfold_ptr(t);
>
> + /*
> + * preallocated cached pages, which is used to avoid direct reclaim
> + * otherwise, it will go inplace I/O path instead.
> + */
> + if (page->private == Z_EROFS_PREALLOCATED_PAGE) {
> + WRITE_ONCE(pcl->compressed_pages[nr], page);
> + set_page_private(page, 0);
> + tocache = true;
> + goto out_tocache;
> + }
> mapping = READ_ONCE(page->mapping);
>
> /*
> @@ -1073,7 +1106,7 @@ static struct page *pickup_page_for_submission(struct z_erofs_pcluster *pcl,
> cond_resched();
> goto repeat;
> }
> -
> +out_tocache:
> if (!tocache || add_to_page_cache_lru(page, mc, index + nr, gfp)) {
> /* turn into temporary page if fails */
> set_page_private(page, Z_EROFS_SHORTLIVED_PAGE);
> @@ -1282,7 +1315,7 @@ static int z_erofs_readpage(struct file *file, struct page *page)
>
> f.headoffset = (erofs_off_t)page->index << PAGE_SHIFT;
>
> - err = z_erofs_do_read_page(&f, page);
> + err = z_erofs_do_read_page(&f, page, &pagepool);
> (void)z_erofs_collector_end(&f.clt);
>
> /* if some compressed cluster ready, need submit them anyway */
> @@ -1336,7 +1369,7 @@ static void z_erofs_readahead(struct readahead_control *rac)
> /* traversal in reverse order */
> head = (void *)page_private(page);
>
> - err = z_erofs_do_read_page(&f, page);
> + err = z_erofs_do_read_page(&f, page, &pagepool);
> if (err)
> erofs_err(inode->i_sb,
> "readahead error at page %lu @ nid %llu",
>
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