Re: [PATCH v2] erofs: relaxed temporary buffers allocation on readahead

[Chunhai Guo via Linux-erofs <linux-erofs@lists.ozlabs.org>]

On 2024/1/22 10:07, Gao Xiang wrote:
> [你通常不会收到来自 hsiangkao@linux.alibaba.com 的电子邮件。请访问 https://aka.ms/LearnAboutSenderIdentification，以了解这一点为什么很重要]
>
> On 2024/1/20 22:55, Chunhai Guo wrote:
>> Even with inplace decompression, sometimes extra temporary buffers are
>> still needed for decompression.  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 memory pressure.
>>
>> There is an average reduction of 21% in page allocation time under
> It would be better to add a table to show the absolute numbers too
> (like what you did in the global pool commit.)  If it's possible, there
> is no need to send a update version for this, just reply the updated
> commit message and I will update the commit manually.


The table below shows detailed numbers. The reduction I mentioned before
was not accurate enough. Please help correct the improvement from 21% to
20.21%.


+--------------+----------------+---------------+---------+
|              | w/o GFP_NOWAIT | w/ GFP_NOWAIT |  diff   |
+--------------+----------------+---------------+---------+
| Average (ms) |     3364       |      2684     | -20.21% |
+--------------+----------------+---------------+---------+

Thanks,


>
> Otherwise it looks good to me,
>
> Thanks,
> Gao Xiang
>
>> multi-app launch benchmark workload [1] on ARM64 Android devices running
>> the 5.15 kernel with an 8-core CPU and 8GB of memory.
>>
>> [1] https://lore.kernel.org/r/20240109074143.4138783-1-guochunhai@vivo.com
>>
>> Suggested-by: Gao Xiang <xiang@kernel.org>
>> Signed-off-by: Chunhai Guo <guochunhai@vivo.com>
>> ---
>>    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 1d65b9f60a39..ef2b08ec9830 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 692c0c39be63..a293de2a60ed 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[];
>>    };
>> @@ -964,7 +967,7 @@ 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;
>> @@ -1014,6 +1017,7 @@ 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;
>>        }
>>
>>        /*
>> @@ -1280,7 +1284,11 @@ 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;
>>
>>        /* must handle all compressed pages before actual file pages */
>>        if (z_erofs_is_inline_pcluster(pcl)) {
>> @@ -1785,7 +1793,7 @@ 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);
>>                }
>>
>> @@ -1806,7 +1814,7 @@ 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);
>>
>> @@ -1847,7 +1855,7 @@ 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);