From: Jason Gunthorpe <jgg@ziepe.ca>
To: "Liam R. Howlett" <liam@infradead.org>
Cc: Kiryl Shutsemau <kas@kernel.org>,
"Lorenzo Stoakes (ARM)" <ljs@kernel.org>,
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Hugh Dickins <hughd@google.com>, Qi Zheng <qi.zheng@linux.dev>
Subject: Re: [PATCH 01/12] mm/huge_memory: zap deposited page tables after an RCU grace period
Date: Tue, 1 Sep 2026 13:06:16 -0300 [thread overview]
Message-ID: <20260901160616.GD56830@ziepe.ca> (raw)
In-Reply-To: <kasi4mkjkt56wxsrmphm5o2qfg2lwsdxf3tlmzx5tq6t7uez74@kozleoavd6r2>
On Tue, Sep 01, 2026 at 11:54:47AM -0400, Liam R. Howlett wrote:
> On 26/09/01 04:28PM, Kiryl Shutsemau wrote:
> > On Tue, Sep 01, 2026 at 03:41:17PM +0100, Lorenzo Stoakes (ARM) wrote:
> > > On Tue, Sep 01, 2026 at 11:24:08AM -0300, Jason Gunthorpe wrote:
> > > > On Tue, Sep 01, 2026 at 03:12:45PM +0100, Lorenzo Stoakes (ARM) wrote:
> > > >
> > > > > It won't be costly at the time of the calls obviously as its deferred. Maybe
> > > > > increase some time spent in softirq but again is 512x that big of a deal?
> > > > >
> > > > > I'm not sure how you'd both defer the free and somehow utilise mmu_gather here
> > > > > either really, certainly not without it becoming extremely messy.
> > > >
> > > > The less costly version is to thread the page to be freed onto the
> > > > mmu_gather through a linked list in the struct page memory. This is
> > > > super cheap since it is just a singly linked list operation.
> > > >
> > > > Then when the mmu_gather is flushed it does a single call_rcu using
> > > > the rcu head of the struct page of the head of the list. The callback
> > > > clears the entire linked list of pages.
>
> If you are going through the trouble of doing this on your side with a
> custom rcu callback, it might be better to pack the pointers in a way
> that does not need to pointer chase through a linked list.
Well, I have 8 bytes of memory in a struct page and can't allocate in
these paths, so IDK there is another option..
Jason
next prev parent reply other threads:[~2026-09-01 16:06 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-09-01 11:01 [PATCH 00/12] mm: make userland page table freeing RCU-safe Lorenzo Stoakes (ARM)
2026-09-01 11:01 ` [PATCH 01/12] mm/huge_memory: zap deposited page tables after an RCU grace period Lorenzo Stoakes (ARM)
2026-09-01 11:18 ` sashiko-bot
2026-09-01 13:19 ` Kiryl Shutsemau
2026-09-01 14:12 ` Lorenzo Stoakes (ARM)
2026-09-01 14:24 ` Jason Gunthorpe
2026-09-01 14:41 ` Lorenzo Stoakes (ARM)
2026-09-01 15:28 ` Kiryl Shutsemau
2026-09-01 15:45 ` Lorenzo Stoakes (ARM)
2026-09-01 17:11 ` Kiryl Shutsemau
2026-09-01 17:14 ` Lorenzo Stoakes (ARM)
2026-09-01 15:54 ` Liam R. Howlett
2026-09-01 16:06 ` Jason Gunthorpe [this message]
2026-09-01 17:13 ` Kiryl Shutsemau
2026-09-01 17:47 ` Liam R. Howlett
2026-09-01 11:01 ` [PATCH 02/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for most 2-level architectures Lorenzo Stoakes (ARM)
2026-09-01 11:22 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 03/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU riscv Lorenzo Stoakes (ARM)
2026-09-01 11:14 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 04/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for MMU arm Lorenzo Stoakes (ARM)
2026-09-01 11:18 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 05/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for arc, microblaze, xtensa Lorenzo Stoakes (ARM)
2026-09-01 11:28 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 06/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sparc64 Lorenzo Stoakes (ARM)
2026-09-01 11:23 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 07/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-coldfire Lorenzo Stoakes (ARM)
2026-09-01 11:23 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 08/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sh-X2 Lorenzo Stoakes (ARM)
2026-09-01 11:30 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 09/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for m68k-motorola Lorenzo Stoakes (ARM)
2026-09-01 11:30 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 10/12] mm: enable MMU_GATHER_RCU_TABLE_FREE for sparc32 Lorenzo Stoakes (ARM)
2026-09-01 11:37 ` sashiko-bot
2026-09-01 11:01 ` [PATCH 11/12] mm: make userland page table freeing RCU-safe Lorenzo Stoakes (ARM)
2026-09-01 11:52 ` sashiko-bot
2026-09-01 13:33 ` Kiryl Shutsemau
2026-09-01 14:03 ` Lorenzo Stoakes (ARM)
2026-09-01 11:01 ` [PATCH 12/12] mm: change the contract for free_pgtables(), update docs Lorenzo Stoakes (ARM)
2026-09-01 11:37 ` sashiko-bot
2026-09-01 13:57 ` Kiryl Shutsemau
2026-09-01 14:31 ` Lorenzo Stoakes (ARM)
2026-09-01 17:15 ` Kiryl Shutsemau
2026-09-01 17:25 ` Lorenzo Stoakes (ARM)
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