linux-kernel - Re: [PATCH] mm: Optimize TLB flushes during page reclaim

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Message-ID: <CALf+9Ycp4KBnHy8r9x_gARqdwn7-1dYwutQdzFhHnTMf+GQiZQ@mail.gmail.com>
Date: Wed, 22 Jan 2025 07:28:56 -0600
From: Vinay Banakar <vny@...gle.com>
To: Bharata B Rao <bharata@....com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org, 
	akpm@...ux-foundation.org, willy@...radead.org, mgorman@...e.de, 
	Wei Xu <weixugc@...gle.com>, Greg Thelen <gthelen@...gle.com>
Subject: Re: [PATCH] mm: Optimize TLB flushes during page reclaim

On Wed, Jan 22, 2025 at 2:59 AM Bharata B Rao <bharata@....com> wrote:
> While that may be true for MADV_PAGEOUT path, does the same assumption
> hold good for other paths from which shrink_folio_list() gets called?

shrink_folio_list() is called by three other functions, each with
different batching behavior:
- reclaim_clean_pages_from_list(): Doesn't do PMD batching but only
processes clean pages, so it won't take the path affected by this
patch. This is called from the contiguous memory allocator
(cma_alloc#alloc_contig_range)
- shrink_inactive_list(): Reclaims inactive pages at SWAP_CLUSTER_MAX
(default 32) at a time. With this patch, we will reduce IPIs for TLB
flushes by a factor of 32 in kswapd
- evict_folios(): In the MGLRU case, the number of pages
shrink_folio_list() processes can vary between 64 (MIN_LRU_BATCH) and
4096 (MAX_LRU_BATCH). The reduction in IPIs will vary accordingly

Thanks!
Vinay