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b=xRUGLhICw2vX5I4094xI6IGb/XFIq0lvsgePX5F4YnkiIfZZIwY7a4oaZNw7GUPAG ZLhBdp7zomiVO9PE+/f8ol5ENNC2WgwXisDQqEQQmYm9ub3ero1Exc25y86Vy9Qmfx aRSuZ/NKksk20yHPCpn4lK+rueAPErWb2u4NK2mM= Date: Wed, 6 Nov 2024 13:03:18 -0800 From: Andrew Morton To: Yafang Shao Cc: willy@infradead.org, linux-mm@kvack.org Subject: Re: [PATCH] mm/readahead: Fix large folio support in async readahead Message-Id: <20241106130318.91f05382d2c0bbd2be3abff5@linux-foundation.org> In-Reply-To: <20241106092114.8408-1-laoar.shao@gmail.com> References: <20241106092114.8408-1-laoar.shao@gmail.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 86F2240025 X-Stat-Signature: g5uowoqiscc1ih4ojyefuyfpmhhhjxgo X-HE-Tag: 1730926984-672708 X-HE-Meta: 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 qeEVxG4U wgP4Nnp26ae5dZxdVw+jT9GMpdovTiAWA3ceDiovHa2TMJg/FvTzlJk9HL9DwxToILph3sodW/uNJjZa8T+jvg+P0HBTIbLEkdkiT1ii+tO+XD+oNE6Rz85oearHInL8jowuLmZQm8ZlN30dAG1Y84yng/9AtZ74GoWCUA1dEbJCoWyhffPzYEWD7SO4Rq6Tif1CvClHOX75ak8yt4NFnud5mNlwaIQrfW2TAZN9vOOO77CUyFXaS94IC63YN/jFpJO8mseA/jfjdYV+ftNiFOtmP2vksTtYBZWiR0+5m8M2jj9Y= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, 6 Nov 2024 17:21:14 +0800 Yafang Shao wrote: > When large folio support is enabled and read_ahead_kb is set to a smaller > value, ra->size (4MB) may exceed the maximum allowed size (e.g., 128KB). To > address this, we need to add a conditional check for such cases. However, > this alone is insufficient, as users might set read_ahead_kb to a larger, > non-hugepage-aligned value (e.g., 4MB + 128KB). In these instances, it is > essential to explicitly align ra->size with the hugepage size. How much performance improvement is this likely to offer our users? IOW, should we consider backporting it? (I bet anyone who comes across this will say "oh goody" and backport it anyway, so why not do this for them?)