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Date: Thu, 19 Oct 2023 16:15:08 +0200
From: David Hildenbrand <david@...hat.com>
To: Zhiguo Jiang <justinjiang@...o.com>,
Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Cc: opensource.kernel@...o.com
Subject: Re: [PATCH v2 1/2] mm:vmscan: the dirty folio in folio_list skip
unmap
On 19.10.23 15:14, Zhiguo Jiang wrote:
> In the shrink_folio_list() the sources of the file dirty folio include
> two ways below:
> 1. The dirty folio is from the incoming parameter folio_list,
> which is the inactive file lru.
> 2. The dirty folio is from the PTE dirty bit transferred by
> the try_to_unmap().
>
> For the first source of the dirty folio, if the dirty folio does not
> support pageout, the dirty folio can skip unmap in advance to reduce
> recyling time.
>
> Signed-off-by: Zhiguo Jiang <justinjiang@...o.com>
> ---
>
> Changelog:
> v1->v2:
> 1. Keep the original judgment flow.
> 2. Add the interface of folio_check_pageout().
> 3. The dirty folio which does not support pageout in inactive file lru
> skip unmap in advance.
>
> mm/vmscan.c | 103 +++++++++++++++++++++++++++++++++-------------------
> 1 file changed, 66 insertions(+), 37 deletions(-)
>
> diff --git a/mm/vmscan.c b/mm/vmscan.c
> index a68d01fcc307..e067269275a5 100755
> --- a/mm/vmscan.c
> +++ b/mm/vmscan.c
> @@ -925,6 +925,44 @@ static void folio_check_dirty_writeback(struct folio *folio,
> mapping->a_ops->is_dirty_writeback(folio, dirty, writeback);
> }
>
> +/* Check if a dirty folio can support pageout in the recyling process*/
> +static bool folio_check_pageout(struct folio *folio,
> + struct pglist_data *pgdat)
> +{
> + int ret = true;
> +
> + /*
> + * Anonymous folios are not handled by flushers and must be written
> + * from reclaim context. Do not stall reclaim based on them.
> + * MADV_FREE anonymous folios are put into inactive file list too.
> + * They could be mistakenly treated as file lru. So further anon
> + * test is needed.
> + */
> + if (!folio_is_file_lru(folio) ||
> + (folio_test_anon(folio) && !folio_test_swapbacked(folio)))
> + goto out;
> +
> + if (folio_test_dirty(folio) &&
> + (!current_is_kswapd() ||
> + !folio_test_reclaim(folio) ||
> + !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
> + /*
> + * Immediately reclaim when written back.
> + * Similar in principle to folio_deactivate()
> + * except we already have the folio isolated
> + * and know it's dirty
> + */
> + node_stat_mod_folio(folio, NR_VMSCAN_IMMEDIATE,
> + folio_nr_pages(folio));
> + folio_set_reclaim(folio);
> +
> + ret = false;
> + }
> +
> +out:
> + return ret;
> +}
> +
> static struct folio *alloc_demote_folio(struct folio *src,
> unsigned long private)
> {
> @@ -1078,6 +1116,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
> if (dirty && !writeback)
> stat->nr_unqueued_dirty += nr_pages;
>
> + /* If the dirty folio dose not support pageout,
> + * the dirty folio can skip this recycling.
> + */
> + if (!folio_check_pageout(folio, pgdat))
> + goto activate_locked;
> +
> /*
> * Treat this folio as congested if folios are cycling
> * through the LRU so quickly that the folios marked
> @@ -1261,43 +1305,6 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
> enum ttu_flags flags = TTU_BATCH_FLUSH;
> bool was_swapbacked = folio_test_swapbacked(folio);
>
> - if (folio_test_dirty(folio)) {
> - /*
> - * Only kswapd can writeback filesystem folios
> - * to avoid risk of stack overflow. But avoid
> - * injecting inefficient single-folio I/O into
> - * flusher writeback as much as possible: only
> - * write folios when we've encountered many
> - * dirty folios, and when we've already scanned
> - * the rest of the LRU for clean folios and see
> - * the same dirty folios again (with the reclaim
> - * flag set).
> - */
> - if (folio_is_file_lru(folio) &&
> - (!current_is_kswapd() ||
> - !folio_test_reclaim(folio) ||
> - !test_bit(PGDAT_DIRTY, &pgdat->flags))) {
> - /*
> - * Immediately reclaim when written back.
> - * Similar in principle to folio_deactivate()
> - * except we already have the folio isolated
> - * and know it's dirty
> - */
> - node_stat_mod_folio(folio, NR_VMSCAN_IMMEDIATE,
> - nr_pages);
> - folio_set_reclaim(folio);
> -
> - goto activate_locked;
> - }
> -
> - if (references == FOLIOREF_RECLAIM_CLEAN)
> - goto keep_locked;
> - if (!may_enter_fs(folio, sc->gfp_mask))
> - goto keep_locked;
> - if (!sc->may_writepage)
> - goto keep_locked;
> - }
> -
> if (folio_test_pmd_mappable(folio))
> flags |= TTU_SPLIT_HUGE_PMD;
>
> @@ -1323,6 +1330,28 @@ static unsigned int shrink_folio_list(struct list_head *folio_list,
>
> mapping = folio_mapping(folio);
> if (folio_test_dirty(folio)) {
> + /*
> + * Only kswapd can writeback filesystem folios
> + * to avoid risk of stack overflow. But avoid
> + * injecting inefficient single-folio I/O into
> + * flusher writeback as much as possible: only
> + * write folios when we've encountered many
> + * dirty folios, and when we've already scanned
> + * the rest of the LRU for clean folios and see
> + * the same dirty folios again (with the reclaim
> + * flag set).
> + */
> + if (folio_is_file_lru(folio) &&
> + !folio_check_pageout(folio, pgdat))
> + goto activate_locked;
> +
> + if (references == FOLIOREF_RECLAIM_CLEAN)
> + goto keep_locked;
> + if (!may_enter_fs(folio, sc->gfp_mask))
> + goto keep_locked;
> + if (!sc->may_writepage)
> + goto keep_locked;
> +
> /*
> * Folio is dirty. Flush the TLB if a writable entry
> * potentially exists to avoid CPU writes after I/O
I'm confused. Did you apply this on top of v1 by accident?
--
Cheers,
David / dhildenb
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