From: Pedro Falcato <pfalcato@suse•de>
To: Usama Arif <usama.arif@linux•dev>
Cc: Andrew Morton <akpm@linux-foundation•org>,
david@kernel•org, willy@infradead•org, ryan.roberts@arm•com,
linux-mm@kvack•org, r@hev•cc, jack@suse•cz,
Andrew Donnellan <andrew+kernel@donnellan•id.au>,
apopple@nvidia•com, baohua@kernel•org,
baolin.wang@linux•alibaba.com, brauner@kernel•org,
catalin.marinas@arm•com, dev.jain@arm•com, kees@kernel•org,
kevin.brodsky@arm•com, lance.yang@linux•dev,
"Liam R. Howlett" <liam@infradead•org>,
linux-arm-kernel@lists•infradead.org,
linux-fsdevel@vger•kernel.org, linux-kernel@vger•kernel.org,
ljs@kernel•org, mhocko@suse•com, npache@redhat•com,
pasha.tatashin@soleen•com, rmclure@linux•ibm.com,
rppt@kernel•org, surenb@google•com, vbabka@kernel•org,
Al Viro <viro@zeniv•linux.org.uk>,
ziy@nvidia•com, hannes@cmpxchg•org, kas@kernel•org,
shakeel.butt@linux•dev, kernel-team@meta•com
Subject: Re: [PATCH v7 2/2] mm: use mapping_max_folio_order() for force_thp_readahead order
Date: Thu, 4 Jun 2026 20:33:23 +0100 [thread overview]
Message-ID: <aiHSt1uK3ESOU-2O@pedro-suse> (raw)
In-Reply-To: <20260601102205.3985788-3-usama.arif@linux.dev>
On Mon, Jun 01, 2026 at 03:21:18AM -0700, Usama Arif wrote:
> The force_thp_readahead path in do_sync_mmap_readahead() is gated on
> HPAGE_PMD_ORDER <= MAX_PAGECACHE_ORDER and always requests
> HPAGE_PMD_ORDER / HPAGE_PMD_NR. On configurations where HPAGE_PMD_ORDER
> exceeds MAX_PAGECACHE_ORDER, notably arm64 with a 64K base page size,
> VM_HUGEPAGE mappings cannot use this path and fall back to the non-forced
> mmap readahead path even when the mapping supports useful large folios.
>
> Enable forced readahead for mappings that support large folios and request
> the max folio order supported by the mapping, capped at 2M.
> 2MB is chosen as the cap because it matches the PMD size on x86_64
> and on arm64 with 4K base pages, so the size/memory-pressure tradeoff
> for folios of that size is already well understood. On arm64 with 16K
> and 64K base page sizes, 2MB is also the contiguous-PTE (contpte)
> block size, so the resulting folios coalesce into a single TLB entry
> and reduce TLB pressure on the readahead path. This will result
> in 32M folios not being faulted in with 16K base page size for arm64,
> but with contpte, the performance difference should be negligible.
>
> The final allocation order may still be clamped by page_cache_ra_order()
> to the mapping and request geometry, but this gives VM_HUGEPAGE mappings
> on such configurations a large-folio readahead request instead of
> dropping back to base-page readahead.
>
> Signed-off-by: Usama Arif <usama.arif@linux•dev>
Reviewed-by: Pedro Falcato <pfalcato@suse•de>
Overall LGTM. Lets see if performance doesn't degrade.
/me hides in cover
--
Pedro
next prev parent reply other threads:[~2026-06-04 19:33 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-01 10:21 [PATCH v7 0/2] mm: improve large folio readahead for exec memory Usama Arif
2026-06-01 10:21 ` [PATCH v7 1/2] mm: bypass mmap_miss heuristic for VM_EXEC readahead Usama Arif
2026-06-02 3:51 ` Oscar Salvador (SUSE)
2026-06-04 19:30 ` Pedro Falcato
2026-06-01 10:21 ` [PATCH v7 2/2] mm: use mapping_max_folio_order() for force_thp_readahead order Usama Arif
2026-06-01 16:22 ` Jan Kara
2026-06-04 19:33 ` Pedro Falcato [this message]
2026-06-01 23:10 ` [PATCH v7 0/2] mm: improve large folio readahead for exec memory Andrew Morton
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