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Date: Fri, 26 Jan 2024 18:46:56 +0800
From: Yue Hu <zbestahu@...il.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: linux-erofs@...ts.ozlabs.org, LKML <linux-kernel@...r.kernel.org>, Yue
Hu <huyue2@...lpad.com>, Chunhai Guo <guochunhai@...o.com>
Subject: Re: [PATCH v3] erofs: relaxed temporary buffers allocation on
readahead
On Fri, 26 Jan 2024 13:36:16 +0800
Gao Xiang <hsiangkao@...ux.alibaba.com> wrote:
> From: Chunhai Guo <guochunhai@...o.com>
>
> Even with inplace decompression, sometimes very few temporary buffers
> are still needed for a single decompression shot (e.g. 16 pages for 64k
> sliding window or 4 pages for 16k sliding window). In low-memory
> scenarios, it would be better to try to allocate with GFP_NOWAIT on
> readahead first. That can help reduce the time spent on page allocation
> under durative memory pressure.
>
> Here are detailed performance numbers under multi-app launch benchmark
> workload [1] on ARM64 Android devices (8-core CPU and 8GB of memory)
> running a 5.15 LTS kernel with EROFS of 4k pclusters:
>
> +----------------+---------+---------+---------+
> | LZ4 | vanilla | patched | diff |
> |----------------+---------+---------+---------|
> | Average (ms) | 3364 | 2684 | -20.21% | [64k sliding window]
> |----------------+---------+---------+---------|
> | Average (ms) | 2079 | 1610 | -22.56% | [16k sliding window]
> +----------------+---------+---------+---------+
>
> The total size of system images for 4k pcluster is almost unchanged:
> (64k sliding window) 9,117,044 KB
> (16k sliding window) 9,113,096 KB
>
> Therefore, in addition to switch the sliding window from 64k to 16k,
> after applying this patch, it can eventually save 52.14% (3364 -> 1610)
> on average with no memory reservation. That is particularly useful for
> embedded devices with limited resources.
>
> [1] https://lore.kernel.org/r/20240109074143.4138783-1-guochunhai@vivo.com
>
> Suggested-by: Gao Xiang <xiang@...nel.org>
> Signed-off-by: Chunhai Guo <guochunhai@...o.com>
> Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> ---
> v2: https://lore.kernel.org/r/20240120145551.1941483-1-guochunhai@vivo.com
> change since v2:
> - update commit message according to test results.
>
> I plan to apply this version.
>
> fs/erofs/compress.h | 5 ++---
> fs/erofs/decompressor.c | 5 +++--
> fs/erofs/decompressor_deflate.c | 19 +++++++++++++------
> fs/erofs/decompressor_lzma.c | 17 ++++++++++++-----
> fs/erofs/zdata.c | 16 ++++++++++++----
> 5 files changed, 42 insertions(+), 20 deletions(-)
>
> diff --git a/fs/erofs/compress.h b/fs/erofs/compress.h
> index 279933e007d2..7cc5841577b2 100644
> --- a/fs/erofs/compress.h
> +++ b/fs/erofs/compress.h
> @@ -11,13 +11,12 @@
> struct z_erofs_decompress_req {
> struct super_block *sb;
> struct page **in, **out;
> -
> unsigned short pageofs_in, pageofs_out;
> unsigned int inputsize, outputsize;
>
> - /* indicate the algorithm will be used for decompression */
> - unsigned int alg;
> + unsigned int alg; /* the algorithm for decompression */
> bool inplace_io, partial_decoding, fillgaps;
> + gfp_t gfp; /* allocation flags for extra temporary buffers */
> };
>
> struct z_erofs_decompressor {
> diff --git a/fs/erofs/decompressor.c b/fs/erofs/decompressor.c
> index 072ef6a66823..d4cee95af14c 100644
> --- a/fs/erofs/decompressor.c
> +++ b/fs/erofs/decompressor.c
> @@ -111,8 +111,9 @@ static int z_erofs_lz4_prepare_dstpages(struct z_erofs_lz4_decompress_ctx *ctx,
> victim = availables[--top];
> get_page(victim);
> } else {
> - victim = erofs_allocpage(pagepool,
> - GFP_KERNEL | __GFP_NOFAIL);
> + victim = erofs_allocpage(pagepool, rq->gfp);
> + if (!victim)
> + return -ENOMEM;
> set_page_private(victim, Z_EROFS_SHORTLIVED_PAGE);
> }
> rq->out[i] = victim;
> diff --git a/fs/erofs/decompressor_deflate.c b/fs/erofs/decompressor_deflate.c
> index 4a64a9c91dd3..b98872058abe 100644
> --- a/fs/erofs/decompressor_deflate.c
> +++ b/fs/erofs/decompressor_deflate.c
> @@ -95,7 +95,7 @@ int z_erofs_load_deflate_config(struct super_block *sb,
> }
>
> int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
> - struct page **pagepool)
> + struct page **pgpl)
> {
> const unsigned int nrpages_out =
> PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
> @@ -158,8 +158,12 @@ int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
> strm->z.avail_out = min_t(u32, outsz, PAGE_SIZE - pofs);
> outsz -= strm->z.avail_out;
> if (!rq->out[no]) {
> - rq->out[no] = erofs_allocpage(pagepool,
> - GFP_KERNEL | __GFP_NOFAIL);
> + rq->out[no] = erofs_allocpage(pgpl, rq->gfp);
> + if (!rq->out[no]) {
> + kout = NULL;
> + err = -ENOMEM;
> + break;
> + }
> set_page_private(rq->out[no],
> Z_EROFS_SHORTLIVED_PAGE);
> }
> @@ -211,8 +215,11 @@ int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
>
> DBG_BUGON(erofs_page_is_managed(EROFS_SB(sb),
> rq->in[j]));
> - tmppage = erofs_allocpage(pagepool,
> - GFP_KERNEL | __GFP_NOFAIL);
> + tmppage = erofs_allocpage(pgpl, rq->gfp);
> + if (!tmppage) {
> + err = -ENOMEM;
> + goto failed;
> + }
> set_page_private(tmppage, Z_EROFS_SHORTLIVED_PAGE);
> copy_highpage(tmppage, rq->in[j]);
> rq->in[j] = tmppage;
> @@ -230,7 +237,7 @@ int z_erofs_deflate_decompress(struct z_erofs_decompress_req *rq,
> break;
> }
> }
> -
> +failed:
> if (zlib_inflateEnd(&strm->z) != Z_OK && !err)
> err = -EIO;
> if (kout)
> diff --git a/fs/erofs/decompressor_lzma.c b/fs/erofs/decompressor_lzma.c
> index 2dd14f99c1dc..6ca357d83cfa 100644
> --- a/fs/erofs/decompressor_lzma.c
> +++ b/fs/erofs/decompressor_lzma.c
> @@ -148,7 +148,7 @@ int z_erofs_load_lzma_config(struct super_block *sb,
> }
>
> int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
> - struct page **pagepool)
> + struct page **pgpl)
> {
> const unsigned int nrpages_out =
> PAGE_ALIGN(rq->pageofs_out + rq->outputsize) >> PAGE_SHIFT;
> @@ -215,8 +215,11 @@ int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
> PAGE_SIZE - pageofs);
> outlen -= strm->buf.out_size;
> if (!rq->out[no] && rq->fillgaps) { /* deduped */
> - rq->out[no] = erofs_allocpage(pagepool,
> - GFP_KERNEL | __GFP_NOFAIL);
> + rq->out[no] = erofs_allocpage(pgpl, rq->gfp);
> + if (!rq->out[no]) {
> + err = -ENOMEM;
> + break;
> + }
> set_page_private(rq->out[no],
> Z_EROFS_SHORTLIVED_PAGE);
> }
> @@ -258,8 +261,11 @@ int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
>
> DBG_BUGON(erofs_page_is_managed(EROFS_SB(rq->sb),
> rq->in[j]));
> - tmppage = erofs_allocpage(pagepool,
> - GFP_KERNEL | __GFP_NOFAIL);
> + tmppage = erofs_allocpage(pgpl, rq->gfp);
> + if (!tmppage) {
> + err = -ENOMEM;
> + goto failed;
> + }
> set_page_private(tmppage, Z_EROFS_SHORTLIVED_PAGE);
> copy_highpage(tmppage, rq->in[j]);
> rq->in[j] = tmppage;
> @@ -277,6 +283,7 @@ int z_erofs_lzma_decompress(struct z_erofs_decompress_req *rq,
> break;
> }
> }
> +failed:
> if (no < nrpages_out && strm->buf.out)
> kunmap(rq->out[no]);
> if (ni < nrpages_in)
> diff --git a/fs/erofs/zdata.c b/fs/erofs/zdata.c
> index c1c77166b30f..1d0fdc145fd6 100644
> --- a/fs/erofs/zdata.c
> +++ b/fs/erofs/zdata.c
> @@ -82,6 +82,9 @@ struct z_erofs_pcluster {
> /* L: indicate several pageofs_outs or not */
> bool multibases;
>
> + /* L: whether extra buffer allocations are best-effort */
> + bool besteffort;
> +
> /* A: compressed bvecs (can be cached or inplaced pages) */
> struct z_erofs_bvec compressed_bvecs[];
> };
> @@ -960,7 +963,7 @@ static int z_erofs_read_fragment(struct super_block *sb, struct page *page,
> }
>
> static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
> - struct page *page)
> + struct page *page, bool ra)
> {
> struct inode *const inode = fe->inode;
> struct erofs_map_blocks *const map = &fe->map;
> @@ -1010,6 +1013,7 @@ static int z_erofs_do_read_page(struct z_erofs_decompress_frontend *fe,
> err = z_erofs_pcluster_begin(fe);
> if (err)
> goto out;
> + fe->pcl->besteffort |= !ra;
> }
>
> /*
> @@ -1276,7 +1280,11 @@ static int z_erofs_decompress_pcluster(struct z_erofs_decompress_backend *be,
> .inplace_io = overlapped,
> .partial_decoding = pcl->partial,
> .fillgaps = pcl->multibases,
> + .gfp = pcl->besteffort ?
> + GFP_KERNEL | __GFP_NOFAIL :
> + GFP_NOWAIT | __GFP_NORETRY
> }, be->pagepool);
> + pcl->besteffort = false;
reposition it following `pcl->multibases = false`?
>
> /* must handle all compressed pages before actual file pages */
> if (z_erofs_is_inline_pcluster(pcl)) {
> @@ -1787,7 +1795,7 @@ static void z_erofs_pcluster_readmore(struct z_erofs_decompress_frontend *f,
> if (PageUptodate(page))
> unlock_page(page);
> else
> - (void)z_erofs_do_read_page(f, page);
> + (void)z_erofs_do_read_page(f, page, !!rac);
> put_page(page);
> }
>
> @@ -1808,7 +1816,7 @@ static int z_erofs_read_folio(struct file *file, struct folio *folio)
> f.headoffset = (erofs_off_t)folio->index << PAGE_SHIFT;
>
> z_erofs_pcluster_readmore(&f, NULL, true);
> - err = z_erofs_do_read_page(&f, &folio->page);
> + err = z_erofs_do_read_page(&f, &folio->page, false);
> z_erofs_pcluster_readmore(&f, NULL, false);
> z_erofs_pcluster_end(&f);
>
> @@ -1849,7 +1857,7 @@ static void z_erofs_readahead(struct readahead_control *rac)
> folio = head;
> head = folio_get_private(folio);
>
> - err = z_erofs_do_read_page(&f, &folio->page);
> + err = z_erofs_do_read_page(&f, &folio->page, true);
> if (err && err != -EINTR)
> erofs_err(inode->i_sb, "readahead error at folio %lu @ nid %llu",
> folio->index, EROFS_I(inode)->nid);
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